This startup parameter has been applied to all of the 1.13.2 and 1.14 options on the control panel that are tagged as such (ie they literally say [--forceUpgrade] on the jar list. It was applied to all of the 1.13.2/1.14 options in general but as it is causing issues/confusing people it has been changed a bit so there are now two options for each - one with and one without the flag. If you load your server on the options with the flag then it will upgrade all chunks on your server on server restart to the 1.13.2/1.14 chunk formatting on server restart - rather than as you explore and load those chunks in which can cause higher spikes in CPU usage (which is already a major issue in 1.13+). If you have particularly large worlds for it to check this can take a little while on the first run but it should be left to run - it should also be noted that if you are on 1.12.2 and are planning on updating to 1.14 please run it on 1.13.2 first and allow the chunks to upgrade and then go up to 1.14 and allow the chunks to upgrade again, rather than a direct 1.12.2 > 1.14 update (this being recommended by the Spigot team themselves). Once you have ran the upgrade you can switch back to the jarlist option without the flag applied to it so it does not continue to run - however, if your worlds are not particularly large there is no issues with staying on that option and allowing it to run again. On each subsequent restart with this flag after it has already ran it just checks the chunks quickly to see if any need to be upgraded - if you don't have excessively large worlds this will be quick (an example being a server reported a delay on startup of around 5 minutes, which was only due to it having to check over 5 million chunks, so unless you have a world of that extreme size it won't take long on subsequent restarts). If your world has any chunk issues then the upgrade may hang and get stuck, stopping your server from loading. In this case you will need to use the options without the flag.