It has something to do with Qt it seems or its localization that now spell out the timezone in full instead of the short version
We can see the change is system wide in the localization settings “Country and Language” in system settings for the hour setting.
I agree this is quite terrible, the main issue is upstream.
We might want to add a “custom” lang format to be able to tweak this, but this is not simple.
I had a look at /usr/share/i18n/locales/fr_FR (my local).
They are two dates format defined in LC_TIME section: d_t_fmt and date_format.
The first one seems to correspond to what we had and date_format what we currently have.
Perhaps Qt is now using the more verbose date_format for its long data format.