We have just released version 4.1.4 of OBM's Lightning Connector.
It's a bugfix release of the 4.x branch compatible with Thunderbird 31, 38 and 45; so if you're running this version we advise you to upgrade.
The complete list of fixed issues is:
- OLC-85 Free/Busy did not work in Thunderbird 38+
You can get the latest version directly from obm.org. The upgrade is quick and painless, go ahead and try it out!