I'm trying to upgrade my self-hosted server (Ubuntu 18 04 64 bits) from mysql 5.5/Jira 7.10.2 to mysql 5.7/Jira 8.20 in order to migrate to Jira Cloud.
I did mysql 5.5 -> 5.6 -> 5.7 and my Jira 7.10.2 worked fine. I updated all the apps (Timesheet/Adaptavist scriptrunner) before upgrading to 8.20.
I update Jira to the 8.20 version using the bin, I update the mysql jdbc driver to its latest version and modify the dbconfig.xml accordingly.
I start Jira, everything loads. Scriptrunner is disabled because the version is too old. I update it.
After this step, the scriptrunner pages (all of them) are blank and when I try to reindex, I get a popin with an exception.
If I disable Scriptrunner, reindexing works.
Screenshot of reindexing : 
Screenshot of scriptrunner page :

Any idea?