I’m having the same problem on KDE neon, trying cpulimit now, thanks.
$ lsb_release -a
No LSB modules are available.
Distributor ID: neon
Description: KDE neon User Edition 5.16
$ nextcloud --version
Nextcloud version 2.5.2git
Using Qt 5.12.3, built against Qt 5.9.5
Using 'OpenSSL 1.1.1 11 Sep 2018'
Please contribute to these topic if your problem is related, if not please open a new issue. Workarounds are a nice thing to fix something temporarily but please make sure the developers are aware of the problem and can solve it.