I and several people from my game group have the same "fixing rights" problems. NO Antivir- or other security Software, except windows defender. Clean Windows installation (in my case even the 2nd clean windows installation, and the same problems). Its so frustrating. After moving from FG classic to FGU there was barely a week without problems, problem fixing and workarounds.... the whole group seems to spend more time to keep the software running/functional than actually playing the game we love.
My whole group is angry and pushing to change from Fantasy Grounds back to Roll20. After i literally spent YEARS to change their minds about Fantasy Grounds and to stop using Roll20 and switch to Fantasy Grounds (classic at that time). And i dont think i can stop them this time from switching again...
Switching from classic to FGU is just a frustrating experience for me, after buying an ultimate license i have nothing but regrets...