I get the following error every time I open a unity project
"It looks like another Unity instance is running with this project open. Multiple Unity instances cannot open the same project. "
I don’t remember opening multiple instances, and I get the same error when quitting all unities from the dock.
I tried the following but it didn’t work
1 Mac restart&system shutdown
2 Delete Temp / Unity Lock File
3 Kill all unity from activity monitor
Over and over again, I’m having this error in multiple projects and I’m really in trouble.Help me.
macOS Big Sur
バージョン11.5.2
MacBook Pro (13-inch, 2018, Four Thunderbolt 3 Ports)
I was getting this error every time I tried attaching debugger from Rider to Unity. Turns out in Rider there was a “Start Unity” configuration selected for some reason
[186931-スクリーンショット-2021-09-30-212715.png|186931]
@unity_531E5397587AC58FDD64 I’d personally suggest going into task manager (something else if it is different for mac) and closing the unity application from there. Once done open the project again, and if it is not solved and a message similar to that pops up, if there is an x button or some other option to close the pop-up, then click it and wait for like a minute or two (more if your system is slow), and if the project still doesn’t start after closing the pop-up, then open the project again, either from the hub or selecting a project folder when prompted. Hopefully this will work, if not please reply so that i or other people may help in case they had experienced this and had found the problem. Much love, and hope this answer helps 
ive had this issue . unity hub will sometimes create multiple projects instead of one.