WP-Admin URL Changes… Unable to Delete Plugins… Reverse Proxy Setup…

Hi, could someone assist please? It’s been days!

I am not certain if it is relevant, but here is a bit of the apache background to the two wordpress sites I’m running (for a multi-national site):
Site A, the reverse proxy server, is at https://example.com/
Site B, the proxied server, is at https://example.com/siteB

I have no issues with Site A, its been a longstanding site. But Site B is the new addition. The system is setup through ProxyPass and Site B works ok except for one part I’ve noticed. I can do most things in WP-Admin, but when I attempt to delete plugins it will throw to a white screen and say something like “Are you sure you want to do this”, and then the URL changes from Site B to Site A.

For example:
On Site B, you click “Delete all the files…” and then white screen with the message above, and then URL https://example.com/siteB/wp-admin… changes to https://example.com/wp-admin…

Also, when trying to save the configurations of one plugin, it does save the new settings, but then throws the user off Site B as well.

I have been extensively trying different configurations with home_url and site_url in wp-config.php on Site B, because I noticed that that altered the issue in an earlier instance/trail of Site B.

If would be very helpful to at least know if this is entirely an apache issue or wordpress issue. I can provide more system information. Please help!