I can’t post memes. I haven’t changed any settings and I am using the upload button. Site does not want to upload my memes. 
Had the same problem for about 2 months than one day… it worked. I changed nothing and the Admins changed nothing, that I know of.
Check if this applies to “meme” only or any upload. I had the “upload” issues, as @Mike164 mentioned - few weeks.. and it just started working again… 
Which browser are you using?
Firefox
I still have the same issues with DuckDuckGo so if I want to upload gifs/images I have to use Chrome