As you noticed that it was reading preferences, then a high chance is the preference file is corrupted, as opposed to a lock file in place. But, I will share two links, first for restoring (a.k.a resetting) the preference file, second for checking for and deleting a lock file. In (ref 1) a manual method to accomplish this is included.
The preference file can get corrupted leading to buggy behavior. The preference file will survive updates, upgrades, uninstall, reinstall. While restoring the preference file is not primarily meant to reset preferences to defaults, it may. Basically You Are deleting the Preference file, then LrC recreates a new one upon launch.
When you start LrC, it creates a lock file, When you close LrC, it deletes that lock file. Purpose of lock file is to prevent using the catalog twice at the same time. If LrC ct]rashed, or was forced to quit, then the lick file presence prevents that catalog from being opened. LrC is not consistent with displaying an error message when this occurs. In (ref 2) this is discussed, be very very careful.