Site down after Upgrade to 6.3.1b2 and changing active skin
Installation and Configuration
When you run the integrity check there is no need to check the "optimize tables" option unless you have delete A LOT of data from the underlying system. This makes it so a temp table has to be created for the table to be re-written to as the now-missing space in the table is removed/compacted. If you are on SHARED hosting this could make things go really slow.
Here's how to run an offline integrity check + cache reset:
https://www.jamroom.net/the-jamroom-network/documentation/troubleshooting/114/somethings-wrong-what-do-i-do#if-you-cannot-get-in-to-the-acp
Run that and give that time to complete and see if that works.
Hope this helps!