They seem to be fine and ffmpeg processes them correctly. I even re-muxed them using ffmpeg and reuploaded them, but they are still reported with zero duration. An exhaustive list based on recent dump:

https://commons.wikimedia.org/wiki/File:01_-_Gute_Nacht_(CK_2946-2,_ES_383).flac
https://commons.wikimedia.org/wiki/File:02_-_Die_Wetterfahne_(CK_2947-2,_ES_383).flac
https://commons.wikimedia.org/wiki/File:03_-_Gefrorene_Tränen_(CK_2948-1,_ER_270).flac
https://commons.wikimedia.org/wiki/File:04_-_Erstarrung_(CK_2949-1,_ER_270).flac
https://commons.wikimedia.org/wiki/File:05_-_Der_Lindenbaum_(CK_2950-2,_ES_384).flac
https://commons.wikimedia.org/wiki/File:06_-_Wasserfluth_(CK_2951-2,_ES_384).flac
https://commons.wikimedia.org/wiki/File:07_-_Auf_dem_Flusse_(CK_2952-2,_ES_385).flac
https://commons.wikimedia.org/wiki/File:08_-_Rückblick_(CK_2953-1,_ES_385).flac
https://commons.wikimedia.org/wiki/File:09_-_Irrlicht_(BK_2954-2,_ES_271).flac
https://commons.wikimedia.org/wiki/File:10_-_Rast_(BK_2955-2,_ER_271).flac
https://commons.wikimedia.org/wiki/File:11_-_Frühlingstraum_(CK_2956-1,_ES_386).flac
https://commons.wikimedia.org/wiki/File:12_-_Einsamkeit_(CK_2957-2,_ES_386).flac
https://commons.wikimedia.org/wiki/File:13_-_Die_Post_(CK_2958-2,_ER_272).flac
https://commons.wikimedia.org/wiki/File:14_-_Der_greise_Kopf_(BK_2959-2,_ER_272).flac
https://commons.wikimedia.org/wiki/File:15_-_Die_Krähe_(CK_2960-2,_ER_274).flac
https://commons.wikimedia.org/wiki/File:16_-_Letzte_Hoffnung_(CL_4400-2,_ES_392).flac
https://commons.wikimedia.org/wiki/File:17_-_Im_Dorfe_(CL_4399-1,_ES_392).flac
https://commons.wikimedia.org/wiki/File:18_-_Der_stürmische_Morgen_(BK_2963-1,_ER_274).flac
https://commons.wikimedia.org/wiki/File:19_-_Täuschung_(BL_4398-2,_ER_275).flac
https://commons.wikimedia.org/wiki/File:1_de_memoir_av_w_mnem_RECORD20210615163541.flac
https://commons.wikimedia.org/wiki/File:20_-_Der_Wegweiser_(CL_4402-1,_ES_393).flac
https://commons.wikimedia.org/wiki/File:21_-_Das_Wirtshaus_(CL_4403-1,_ES_393).flac
https://commons.wikimedia.org/wiki/File:22_-_Mut_(BK_2967-1,_ER_275).flac
https://commons.wikimedia.org/wiki/File:23_-_Die_Nebensonnen_(BL_4401-1,_ER_276).flac
https://commons.wikimedia.org/wiki/File:24_-_Der_Leiermann_(BK_2969-1,_ER_276).flac
https://commons.wikimedia.org/wiki/File:2_2nd_essai_apres_survol_du_dessin_RECORD20210615164455.flac
https://commons.wikimedia.org/wiki/File:3_De_memoire_apres_observation_des_dessins_RECORD20210615164604.flac
https://commons.wikimedia.org/wiki/File:4_Depuis_le_dessin_rappel_du_texte_RECORD20210615165246.flac
https://commons.wikimedia.org/wiki/File:5_Questions20210615165721_RECORD20210615165721.flac
https://commons.wikimedia.org/wiki/File:Bradyporus_dasypus_male.flac
https://commons.wikimedia.org/wiki/File:Canada2021Election-policies_and_politics_of_Iraninans_in_exile.flac
https://commons.wikimedia.org/wiki/File:Chaughara_darbar.flac
https://commons.wikimedia.org/wiki/File:Harmonica_sings_Tourdion.flac
https://commons.wikimedia.org/wiki/File:Harmonica_sings_Uti_vår_hage.flac
https://commons.wikimedia.org/wiki/File:Kolberg_-_German_pronounciation.flac
https://commons.wikimedia.org/wiki/File:Lachmoeweisma20052019.flac
https://commons.wikimedia.org/wiki/File:Lautäußerung_Kaninchen.flac
https://commons.wikimedia.org/wiki/File:Nightingale_Recording_-_Pines_of_Rome.flac
https://commons.wikimedia.org/wiki/File:Pabuteo.flac
https://commons.wikimedia.org/wiki/File:Rethinking-progress.flac
https://commons.wikimedia.org/wiki/File:Schadenfreude-native-german.flac
https://commons.wikimedia.org/wiki/File:Schönheide_Glockenweihe_Januar_2013.flac
https://commons.wikimedia.org/wiki/File:Sounds_of_a_rollicking_House_Rabbit.flac
https://commons.wikimedia.org/wiki/File:Very_close_thunder_cracks.flac
https://commons.wikimedia.org/wiki/File:حقوق_و_آزادی‌ها_پس_از_تمرکززدایی-مهدی_الهاشمی.flac
https://commons.wikimedia.org/wiki/File:Interview_with_AbuSharif_and_Faisal_-_View_of_the_Ahwazi_Democratic_Popular_Front_about_Human_Rights_and_Fundamental_Freedoms.flac
https://commons.wikimedia.org/wiki/File:گفتگو_با_کاوه_آهنگری-_نَقَدِه_و_مدیریت_دموکراتیک_در_شهرهای_چندفرهنگه.flac
https://commons.wikimedia.org/wiki/File:HPR-h4ck3rm1k3-2013-09-22-Whatsinmybag2.flac