I have an idea about what could have happened.
Versions 3.1.8 and 188.8.131.52 were including the wp_session manager 1.1 library and it was storing the temporary sessions in the WP options table. WP session 1.1 has a bug that caused the sessions rows not to purge automatically.
In version 184.108.40.206, I removed the wp session manager library and made a function to remove the _wp_session entries from the wp options table in the database. So if your site was very busy, there could be many many database entries and WordPress could potentially time out while trying to purge them. Once they are purged, it does not try to purge them anymore and the plugin should function normally.
You might have to purge them manually from the sql command in phpMyAdmin
Here is a help page: