Peter van Westen
Cache Cleaner only cleans cache. It has nothing to do with how cache is created. So any issues you have on that side has nothing to do with Cache Cleaner.
Regarding the cleaning of the SG Cache.
It can be that they have changed how to trigger the cache cleaning via their API, which would require changes in Cache Cleaner too. Not sure.
Are you able to clean the SG Cache via their own Joomla plugin?
Shortly after SiteGround forced the move to their SiteTools, I had all sorts of issues (caused by them doing a half-baked job of migrating my sites).
Tech support has been a joke for the last 2-3 years. They have no expertise on Joomla related stuff whatsoever. And the general knowledge on server stuff is bad too.
Their go-to answer is to blame the index.php of your site as the root of all problems. Or - as you mention - blame extensions or anything else outside of their responsibility.
I ran away from SiteGround after years of having them as my host. Up until 2018 it was fine.
That being said: if the SG Cache cleaning now has stopped working, I think I will rather remove it from Cache Cleaner altogether, instead of trying to fi it.
I don't have any warm feelings for trying to keep support for SiteGround specific stuff.
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