Compression or no compression that is the question

[Ulf Parczyk]

Hello,
I am struggling with PS Insights regarding the advices to compress the page.

Serverwise it is done, plugins and htaccess are IMHO correct in this regard. GZIP test sites say that 87% is saved by compression.

Only PS refuses to see that, at least not in a stable manner: Sometimes it does and the next time - a few moments later without changes on my side - I check it again and then it fails to recognize the compression again (even more puzzling, sometimes there are even different results in the same tests in the mobile and desktop display re. compression!?!?) .
So my site swings between poor and ok...
I do not really understand this.
Can someone help me to understand - and helps to improve the whole thing?
Or is PS moody and  erroneous??  :)  Or my server??
Thanks!
Ulf