You can disable the UPnP and mDNS suggestion finders from the UI, Settings->System Settings->Add-on Management->Advanced.
Alternatively you can do it in a config file, see here: UNSUCCESS: openHAB updated from 4.0.2 to 4.1.0 on docker - openhab unresponsive - #16 by Mherwege
mDNS has always been running, also in previous versions of OH, and the suggestion finder does not do active scanning, only listens to what was already happening. That is different for UPnP where an active scan is triggered by the suggestion finder.
If disabling the suggestion finders does not make a difference, these suggestion finders are not the cause of your issue.