After I uploaded a new version of commons:File:Druhý Kirchhoffův zákon.png yesterday, the 400px thumbnail did not update and still shows the previous version.

Cf. the obsolete 400px thumbnail, and an updated 401px thumbnail.

I tried various cache cleans and action=purge at the file description page (and on the thumbnail itself, even though I doubt that should do anything?), nothing helped. (And it show this way from multiple computers/browsers, it does not seem to be a client-side issue.)

I’d think there would be an existing generic issue/tracking task, but I have not found any. Only a similar report at T333042 (and old T206190) and possibly vaguely related T281780.