IDM (Internet Download Manager) plugin may misbehave with isolated browsers. The reason behind this issue is that injected into browsers plugin tries to communicate with main IDM process. The process works from real user and even restarted (by injected code from explorer.exe), if it's not the case. It communicates via DCOM and plugin working from isolated browser can't connect to it because of security access restrictions. Possible solution to this is to disable the plugin and rely on driver downloads interception, it works for any user including isolated ones.