Doesn't surprise me at all, the company I work for has gone all in with AzureAD SSO and that will only work on Edge (edge supplies info for the MS asset verification software that constantly eats my CPU) so now we can't use anything other than Edge for any internal service and need to develop for Edge if we are writing an internal tool.
I would hope this would be obvious to anyone. If your client can highlight which posts you have upvoted in the web and app UI then the fact that your user specifically upvoted that post must be recoverable from the instance server and thus must be recoverable by the instance admins. I would not expect anything different.