If you restart the server while you run a job in Optimizely, the job will remain in running state for ever and it won't stop or finish or start anymore.
the only solution to fix this issue is to find your job in tblScheduledItem table and set IsRunning to false.
Looks like there was a fix for this issue released in EPiServer.CMS.Core 12.5.1: https://world.optimizely.com/support/bug-list/bug/CMS-22374
Pretty sure the problem have reoccured if the old release ever fixed it, running 12.9.2 and the jobs still gets stuck if you end the session before they're done.
Can you stop it with "Stop" button in job details page?