This is a bit of curious question and also some information on what I managed to find out this week.
I run two similar sites using windows/plesk but only one domain with GoDaddy was eligible for the Trustedsite upgrade (the other one is registered in Japan). For the GoDaddy site, I selected the "free" upgrade 10 days ago. All good so far, but then I noticed my page speed went from good to terrible - only on the upgraded site (my Japan site was fine).
No end of tinkering with web.config or other settings would enable the compression that was continuing to working so well with the other site - the only change was "TrustedSite" - it broke mine and seemed to cause the web.config file to be ignored.
So, I removed it, and hey-presto, compression is back on and page speed back to 99.
Is this an intended "feature" of TrustedSite or was there something else possible broken in the back-ground? Note, no other changes and the parallel site hosted exactly the same way did not have problems.
Thank you for posting. TrustedSite does scan your site but this is the first I've heard of to causing issues with site performance. What's the URL of the site that's behaving slowly? Have you tried reaching out to our support team on this yet?
It might be a bit hard to check anything as I have removed the TrustedSite option and so I am not sure what the support team might find. It was worth testing, but the unexpected side-effect was unusual and was the only recent material change. The last two days my site speed score is lifted from low 80's back up to 99-100 for my important pages (and load time is down to around 3 seconds page load time and before it was over 5 seconds), but I did make some other improvements while hunting for a solution to my issue.
The other curios symptom was running page speed analytics on the https version of .co.nz would throw 404 and 500 server errors, but the http version did not.