Servers giving me errors involving my username

Servers giving me errors involving my username.."370H5SV" saying it dosent exist, I cant seem to get my UUID from anywhere...(this includes the website you guys use for logging in) I cannot OP myself on my own server both vanilla and spigot the only way I can OP myself is to edit the OPS.json(I made a valid copy to replace the old one so its a little bit easier), but this is very annoying(I have to do it every time I log On and it would be easier if I just automatically be op) I can't vote on any server because it tells me "Invalid username" I read somewhere that this is a known bug... but I couldn't find it at all so I'm gonna report it and hope you can help Thx for taking the time to read this!