Calendar sync an hour incorrect

[justcosmic1]

Not sure if this is an MPE bug or something to do with Thunderbird which I use as my calendar. However after turning up an hour early for a hospital appointment today I realised that Thunderbird on my Win 7 pro 64bit SP1 laptop had logged the appointment an hour earlier than my phone running lineage OS 14.1.
I have recently been to a time zone that is an hour behind so am wondering if this has something to do with it. However the appointment was originally created prior to travelling.
It may well be that I synced my phone whilst away and that I "OK'd" an update to that appointment without really looking at it, as sync is usually flawless.
Anyway, I should note that subsequent sync operations since returning to my original time zone have not shown up the discrepancy either.
Would be good to get to the bottom of this obviously and thank you for any and all feedback on this.