• Fixed a bug that would remove components from death messages when players were killed by mobs (thanks lexikiq)
• Rewrote how FlatFileDatabase verifies data integrity
• FlatFileDatabase has much better data validation and will repair broken/invalid data much better
• Fixed a bug where FlatFileDatabase users could have their names saved as "null" (names will be fixed the next time the player logs in)
• Added 20~ unit tests for FlatFileDatabaseManager (see notes)
• FlatFileDB now stores the last login of users again (was completely non functional for a while)
• Newly created flat file databases (mcmmo.users file) will have a comment line at the top noting the date the database was created
• Minor performance optimizations to FlatFile database
• mcMMO will once again purge old users if the config option is on (see notes)
• Fixed a bug where FlatFileDatabaseManager didn't properly upgrade older database entries to the newest schema
• The setting to disable the mcMMO user block tracker has been moved from our "hidden config" to persistent_data.yml
• Added 'mcMMO_Region_System.Enabled' to persistent_data.yml (don't touch this setting unless you know what you are doing)
• Removed MHD command (it didn't do anything for a while now)
• Removed UltraPermissions warning
• Updated pl locale (Thanks Mich3l3k)
• Fixed an IllegalPluginAccessException error that could happen during server shutdown
• Minor performance optimizations to misc parts of the codebase
• (API) Added com.gmail.nossr50.database.DatabaseManager.loadPlayerProfile(org.bukkit.OfflinePlayer)
• (API) Deprecated com.gmail.nossr50.database.DatabaseManager.loadPlayerProfile(java.util.UUID, java.lang.String)
• (API) Removed com.gmail.nossr50.database.DatabaseManager.newUser(java.lang.String, java.util.UUID)
• (API) PrimarySkillType will soon be just an enum with nothing special going on
• (API) Deprecated the members of PrimarySkillType use mcMMO::getSkillTools instead, deprecated members will be removed in Tridents & Crossbows (due soon)
• (API) Some members of PrimarySkillType were removed and not deprecated (such as the field constants)

NOTES:
I spent over 26 hours refactoring FlatFileDB and writing unit tests for it, this will ensure that any changes in the code that could break the database are caught at compile time (so long as we have enough tests, could probably use more)
Regarding purging old users on the FlatFileDB, since this wasn't functioning for a while, the last login of users has been reset and if mcMMO hasn't seen that user since this update, it won't purge them as it has no way to know if they are truly an old user
I'm likely going to add SQLite DB as an option in the future, I spent time to fix up the FlatFileDB as some Unit Testing practice.
Ultra Permissions is SAFE to use with mcMMO, disregard previous messages stating otherwise
After getting in contact with the UltraPermissions devs and exhaustive testing, I have concluded that using UltraPermissions is completely safe with mcMMO. The users who had an issue with performance currently have an unknown cause, potentially it is from a plugin using the UltraPermissions API I really can't say without more data. My apologies to the UltraPermissions team for reporting an issue between our two plugins directly, as that is not the case. I would have tested it myself sooner but UltraPermissions was closed source and premium so I wasn't particularly motivated to do so, however I have been given access to the binaries so now I can do all the testing I want if future issues ever arise which I have zero expectations that they will.