Okay it looks like both my suggestions were incorrect.
I've just discussed this with a colleague and now think it could potentially be a bug whereby the Monitored Servers page is displaying healthy connections (green ticks) when there are actually underlying issues.
Would it be possible for you to locate, zip and email the SQL Monitor log files? These should exist on the machine that hosts the web server + base monitoring service.
More information on how to find log files on this help page:
https://documentation.red-gate.com/page ... Id=2296838