[2020] cant add webm files anymore to the signs

Hey, i recently built 2 maps, where i use webm as imagefile for the signs. thos dissapeared now. when i try to renew them in the editor, they dont show up in the file anymore. they appear in the editor, but no url anymore in he actual gbx file then. only a scrumbled part somwhere in the first 2000 bytes.

webm:
http://covertstrike.org/tm/signs/d.p...=snowfall.webm ( sample) >>
gbx file:
<ä _covertstrike-org_tm_signs_d.php?file=snowfall$9
those work in maniaplanet and did work in trackmania 2020 just la couple of days ago.