@fbartels
So sorry, but was short on time and opted to reinstall the cert. to get back to what seems like normal - and so, I have no information to share in-terms of troubleshooting.
That said, and if /or when this happens again, I'll take the time to properly investigate
NB, for what it's worth, I am using Cloudflare API key, of which has always worked without issue in Cloudron, though for some unknown reason, the cert appears to have expired and would no longer renew. And so I performed as roll-over oin the API/Key side of things, then reissued, and everything appears to be back to normal