Gzip doesn't work

Hi. Could you please advise with the following.
I’m trying to enable Gzip compression but I’m getting the following mess after saving preferences:
But if to reload config page you’ll see that it’s enabled now in spite of shown above:
If to look at response headers it says Content-Encoding: gzip, however all checking tools including Google PageSpeed say that Gzip is not enabled. Grav and plugins are updated to latest.
Big thanks in advance.

It turned out that speed test tool’ warning about gzip were regarding just some files and it’s working overall on a site. My apologies. However, that weird error is still occurring, when pressing save after enabling gzip option. Anyway, topic can be deleted. Thanks!