I too am seeing the same problem. The errors seem to have started around the 18th August with the error messages
[18-Aug-2021 14:35:46 Europe/London] PHP Warning: fsockopen(): unable to connect to ssl://spell.roundcube.net:443 (Connection timed out) in /var/www/html/roundcubemail-1.1.4/program/lib/Roundcube/rcube_spellcheck_googie.php on line 87
Other diagnostics:
$ ping -c 10 spell.roundcube.net
PING spell.roundcube.net (82.94.221.250) 56(84) bytes of data.
From 0.et-8-1-0.xr3.3d12.xs4all.net (194.109.5.2) icmp_seq=1 Destination Net Unreachable
--- spell.roundcube.net ping statistics ---
10 packets transmitted, 0 received, +1 errors, 100% packet loss, time 8999ms
I hope that helps fixing the problem