The problem in that there are could be a lot of different reasons for why. I think that most likely they are related to the individual features of your hosting, server, settings and so on. And I suppose that the best way for identifying and elimination of that reasons is addressing to Plesk Support Team for deep investigation.I suppose you can argue that it is worth waiting for but wouldn't it be more useful to figure out why ?
Hmmm... I'm wondering how this can be possible: doesn't the Plesk panel run with its own PHP?Installing php 7.2 completely solved the problem for me...
Well, actually with some "caveat": see Disabling Facebook integration (backend)I don't want to push anybody doing something he might later regret, but... I'm happy with 17.8.10...
# plesk version
Product version: Plesk Onyx 17.5.3 Update #42
# /usr/local/psa/admin/bin/php -v
PHP 5.6.30 (cli) (built: Sep 12 2017 11:11:16)
# plesk version
Product version: Plesk Onyx 17.8.10
# /usr/local/psa/admin/bin/php -v
PHP 7.1.14 (cli) (built: Feb 9 2018 14:36:24) ( NTS )
Feel the difference!