updated to 2.10 the other day from 2.8 and theres a problem with the pngs i upload edits to tumblr and when i export from 2.10 i get an error message thought i was a bad connection and tried again same error message. tried reuploaded a previous export from 2.8 and it worked fine i put that same picture in the new gimp exported like normal and went to upload
error message again the file sizes were about the same and they did not exceed tumblrs file limit dont know if the problem is on this end or tumblrs just looking for step in the right direction

caveat: I do use tumblr

Taking a jpeg and exporting a png from both Gimp 2.8 and Gimp 2.10, then looking at the properties with Imagemagick. There is a difference, the reported print image size(s) bear no relationship to the original jpeg properties. But that was all.

You could try turning off all the options, set the mode to 8 bit RGB. as screenshot:

Might work.

The only other difference, which should not make any difference, is a small change in the colours, presumably due to Gimp 2.10 opening the jpeg in (default) linear light mode.

caveat: I do use tumblr

That should of course be, I do not use tumblr - or anything social media.