I made a few tests (there is an empty line at some point, and a picture is missing the File: prefix) but didn't find out much. I'm inclined to think it may be choking on too many items, because it works just fine if you leave 10 or 20 of them, for example.
I see several special characters in the file names, dunno if it matters.

VE tries to load image data for the gallery with the following API query:

https://commons.wikimedia.org/w/api.php?action=query&format=json&prop=imageinfo&iiprop=url&iiurlwidth=200&iiurlheight=200&titles=File%3ACabri%C3%A8res+et+le+Pic+de+Vissou+01%2Ejpg%7CFile%3AKilldeer+at+Rodeo+Beach%2Ejpg%7CFile%3AKoluvere+m%C3%B5isa+kivisild+1+2014%2Ejpg%7CFile%3AMaria+Laach+Kirche+Gnadenbild+01%2EJPG%7CFile%3AAT-13763+Kuppelfigur+Athene+am+Kunsthistorischen+Museum+8970%2Ejpg%7CFile%3ADelosperma+cooperi+(D%C3%A9losperma+rose)+-+97%2Ejpg%7CFile%3AReichstagsgeb%C3%A4ude+mit+Weihnachtsbaum+bei+Nacht%2C+Berlin%2C+151223%2C+ako%2Ejpg%7CFile%3AYour+motherland+will+never+forget+-+restoration%2Ejpg%7CFile%3A%CE%A4%CF%8D%CE%BC%CF%80%CE%B1%CE%BD%CE%BF+%CE%99%CE%B4%CE%B1%CE%AF%CE%BF%CF%85+%CE%86%CE%BD%CE%B4%CF%81%CE%BF%CF%85+9098+rt%2Ejpg%7CFile%3ANeptune+Amphitrite+mosaic+Herculaneum%2Ejpg%7CFile%3ASagrada+Familia+March+2015-10a%2Ejpg%7CFile%3A%D0%A1%D0%BE%D0%BB%D0%BE%D0%B2%D0%B5%D1%86%D0%BA%D0%B8%D0%B9+%D0%BC%D0%BE%D0%BD%D0%B0%D1%81%D1%82%D1%8B%D1%80%D1%8C%2Ejpg%7CFile%3A7+Collection+Eybl+Great+Britain+-+E%2E+Kealey+-+Women+of+Britain+say+%E2%80%93+GO%2Ejpg%7CFile%3A2014%2E03%2E29%2E-19-Mannheim+Neckarau+Waldpark--Wald-Veilchen%2Ejpg%7CFile%3AChur+Busbahnhof+ext+2015+wide%2Ejpg%7CFile%3ALondon+MMB+%C2%BB1E6+Lightning%2Ejpg%7CFile%3AAT+119587+Jesuitenkirche+Wien+Innenansicht+9213%2Ejpg%7CFile%3AA+Musica+by+Oscar+Pereira+da+Silva+1896%2Ejpg%7CFile%3ABrompton+Oratory+360x180%2C+London%2C+UK+-+Diliff%2Ejpg%7CFile%3ACast+sitting+victim+Pompeii%2Ejpg%7CFile%3AMunich+subway+station+Hasenbergl+2%2EJPG%7CFile%3AAlbert+Bierstadt+-+A+Storm+in+the+Rocky+Mountains%2C+Mt%2E+Rosalie+-+Google+Art+Project%2Ejpg%7CFile%3AJean-L%C3%A9on+G%C3%A9r%C3%B4me+-+The+Carpet+Merchant+-+Google+Art+Project%2Ejpg%7CFile%3ASilesian+-+Moravian+Beskids+in+winter+2014%2EJPG%7CFile%3ABrighton+MMB+34+West+Pier%2Ejpg%7CFile%3ACity+Hall+Antwerp+July+2015-1%2Ejpg%7CFile%3AIvan+%C5%BDabota+-+Portret+starca%2Ejpg%7CFile%3A2014%2E03%2E09%2E-18-Kaefertaler+Wald-Mannheim-Braune+Krabbenspinne-Weibchen%2Ejpg%7CFile%3ALa+Sacra+ammantata+dalla+neve%2Ejpg%7CFile%3ASistema+de+orquestas+y+coros+juveniles+e+infantiles+del+Zulia%2C+Venezuela%2Eogv%7CFile%3A2015-08+playboating+Durance+09%2Ejpg%7CFile%3AAmerican+White+Pelican+(Las+Gallinas+Wildlife+Ponds)%2Ejpg%7CFile%3AChandelier+of+the+nineteenth+century+in+the+Museo+di+Capodimonte+(Napoli)%2Ejpg%7CFile%3APoertschach+Johannes-Brahms-Promenade+Promenadenbad+Rutschenturm+29122015+9896%2Ejpg%7CFile%3ACementerio+de+San+Diego%2C+Quito%2C+Ecuador%2C+2015-07-22%2C+DD+56-58+PAN%2EJPG%7CFile%3ALaon+Cathedral+Interior+360x180%2C+Picardy%2C+France+-+Diliff%2Ejpg%7CFile%3APel%C3%ADcano+pardo+de+las+Gal%C3%A1pagos+(Pelecanus+occidentalis+urinator)%2C+Bah%C3%ADa+Tortuga%2C+isla+Santa+Cruz%2C+islas+Gal%C3%A1pagos%2C+Ecuador%2C+2015-07-26%2C+DD+32%2EJPG%7CFile%3ATonle+Sap+Siem+Reap+Cambodia+Girl-begging-for-money-with-snake-01%2Ejpg%7CFile%3ATr%C3%A9sor+Caelius+plat%2Ejpg%7CFile%3ACeiling+of+Santa+Maria+in+Vallicella+(Rome)%2Ejpg%7CFile%3ASteindorf+Tiffen+Pfarrkirche+roem+Grabbaurelief+tanzende+Maenade+07032015+0373%2Ejpg%7CFile%3A30a+Sammlung+Eybl+Gro%C3%9Fbritannien%2E+Alfred+Leete+(1882%E2%80%931933)+Britons+(Kitchener)+wants+you+(Briten+Kitchener+braucht+Euch)%2E+1914+(Nachdruck)%2C+74+x+50+cm%2E+(Slg%2ENr%2E+552)%2Ejpg%7CFile%3ADokument+odpustowy%2Ejpg%7CFile%3AEurasian+tree+sparrow+at+Tenn%C5%8Dji+Park+in+Osaka%2C+December+2015%2Ejpg%7CFile%3AHelios%2C+Main+figure+(Johannes+Benk)+at+the+Naturhistorisches+Museum%2C+Wien-9958%2Ejpg%7CFile%3AParis+Notre-Dame+East+View+02%2EJPG%7CFile%3AP%C3%BChaj%C3%A4rve+s%C3%B5jatamm+udus%2Ejpg%7CFile%3APanoramic+view+north+from+Ben+Lomond%2Ejpg%7CFile%3ARing+tailed+lemur+portrait%2Ejpg%7CFile%3AAlbert+Bierstadt+-+Among+the+Sierra+Nevada%2C+California+-+Google+Art+Project%2Ejpg%7CFile%3ABieszczady+-+sunrise+from+Chatka+Puchatka+(2)%2Ejpg%7CFile%3A%D0%9F%D0%B0%D0%BD%D0%BE%D1%80%D0%B0%D0%BC%D0%B0+%D0%A2%D0%BE%D0%B1%D0%BE%D0%BB%D1%8C%D1%81%D0%BA%D0%BE%D0%B3%D0%BE+%D0%BA%D1%80%D0%B5%D0%BC%D0%BB%D1%8F+%D1%81+%D0%BC%D1%8B%D1%81%D0%B0+%D0%A7%D1%83%D0%BA%D0%BC%D0%B0%D0%BD%2Ejpg%7CFile%3AHolstentor+in+L%C3%BCbeck+2015%2Ejpg%7CFile%3AMANNapoli+109982+roue+de+la+fortune+memento+mori%2Ejpg%7CFile%3AGentile+da+Fabriano+-+Coronation+of+the+Virgin%2Ejpg%7CFile%3AGazelles+of+Sunset%2Ejpg%7CFile%3AMovement+of+organelles+in+Tradescantia+stamen+hair+cells%2Ewebm%7CFile%3AMunich+airport+winter+panorama+2015%2Ejpg%7CFile%3APoertschach+Johannes-Brahms-Promenade+Promenadenbad+Rutschenturm+25122015+9840+169crop%2Ejpg%7CFile%3AZicht+op+het+IJsselmeer%2E+Locatie+Mirnser+Klif+02%2Ejpg%7CFile%3AArgynnis+adippe+auf+Centaurea+jacea+01%2Ejpg%7CFile%3AIglesia+de+San+Miguel%2C+Jerez+de+la+Frontera%2C+Espa%C3%B1a%2C+2015-12-07%2C+DD+99-101+HDR%2EJPG%7CFile%3ASunflower+head+2015+G1%2Ejpg%7CFile%3APaul-L%C3%B6be-Haus%2C+Westseite%2C+Berlin-Mitte%2C+151223%2C+ako%2Ejpg%7CFile%3APorto+Covo+January+2016-3a%2Ejpg%7CFile%3AVaried+tit+at+Tenn%C5%8Dji+Park+in+Osaka%2C+January+2016%2Ejpg%7CFile%3APorto+Covo+January+2016-7a%2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schofsburg+West-Ansicht+10042015+0755%2Ejpg%7CFile%3AD%C3%BCsseldorf%2C+Rheinturm+--+2015+--+8127%2Ejpg%7CFile%3AIcelandic+Landscape+near+Neskaupsta%C3%B0ur+July+2014%2EJPG%7CFile%3AJacques+Offenbach+by+Nadar%2Ejpg%7CFile%3ALarus+occidentalis+in+flight+(Bodeda+Head)%2Ejpg%7CFile%3AM%C3%BCnster%2C+Park+Sentmaring+--+2015+--+9923%2Ejpg%7CFile%3APoertschach+Hans-Pruscha-Weg+5+Parkhotel+18112015+9110%2Ejpg%7CFile%3ASala+Capitular%2C+Catedral+de+Sevilla%2C+Sevilla%2C+Espa%C3%B1a%2C+2015-12-06%2C+DD+121-123+HDR%2EJPG%7CFile%3ASouq+Waqif%2C+Doha%2C+Catar%2C+2013-08-05%2C+DD+107%2EJPG%7CFile%3A2014+Filtr+powietrza+DEMCiflex%2Ejpg%7CFile%3AISS046-E-3699%2EJPG%7CFile%3AMountain+massif+of+Fj%C3%B8lhaugen+at+Knutevika+in+Senja%2C+Troms%2C+Norway%2C+2015+September%2Ejpg

Now you don't need to know much about programming to tell that this is a ridiculously long URL. Looks like it exceeds Chrome's length limit. But even when the browser can deal with it, the server responds with a "414 Request-URI Too Long" error. And even if that did not happen, the API will only accept 50 page titles in the 'titles' parameter (there are 158 here).

VE should make separate requests for the data, in chunks of 50 files, and possibly it should send the titles as POST body rather than GET query parameters (someone should look into browsers' and our servers' length limits to see if/when this is necessary).

Change 313605 had a related patch set uploaded (by Alex Monk):
Batch gallery imageinfo requests via ImageInfoCache subclass

https://gerrit.wikimedia.org/r/313605

Change 313605 merged by jenkins-bot:
Batch gallery imageinfo requests via ImageInfoCache subclass

https://gerrit.wikimedia.org/r/313605