Hmm... I've seen some really weird things happening within the latest release of Zorin 12. Will experiment with the site on my end to see if I can replicate the issue in a VM. So far, not having this issue on Linux Mint.EDIT--
Actually, just noticed this bit of weirdness on my Windows Enterprise computer. Was inserting images in another thread and every time I would add the first one, then type text below and before I could add the second one, it would act as if I had hit Page Back. Ended up having to finish the post with Firefox.
Definitely looks like something is broken within Vivaldi. Hopefully, they patch it soon whatever it is.