[R] Custom flags getting overpixelated?

[Aldarminia]

The flags for at least the three nations below are being displayed with a lot more pixelation than normal.

Aldarminia
The Hvalheim
The Raian Mnemarchon

Normal (screenshot from another user):
https://cdn.discordapp.com/attachments/451166193223729162/968073612202504212/unknown.png

Overpixelated (screenshot by me):
https://cdn.discordapp.com/attachments/451166193223729162/968083893087514624/Screenshot_4.png

As far as I can tell the overpixelation (overcompresssion? Idk the technical term, sorry) affects the nation page flag and the forum thumbnail flag. I tried reuploading, adjusting file resolution, clearing cache, fiddling with ripple, etc. Two other nations of mine's (Gvoroska and Vrotomyra) flags are fine* but the three above aren't for some reason. All flags are in PNG format, and I'm using up-to-date Chrome AFAICT. The person who screenshotted the normal example for me doesn't seem to have the issue on their end, but I can't seem to find the fix on mine.

*Edit: It seems like Gvoroska's might be affected too now