Jan,
I got a PM about restarting Solr as a possible solution but I had zero success with it. I don't know if it may work for you:
"restart solr /opt/solr/bin/.restart solr"
but my reply to the sender was as follows:
"
Thanks for this but I’m not getting the syntax to work. I’m unsure of what I’m doing wrong. I have done a ‘systemctl stop solr’ in the past and have navigated into the bin folder for solr and ran ‘./solr stop -p 8983’ to get it to stop and the converse to get it started once more."
If you've had any progress Jan, please feel free to share. I'm pretty stumped.
Cheers.
Lisle