How to remove stuck cranks?

I went to install a new chainring on my raceface aeffect cranks, and in the process this little washer fell out without me noticing. I reinstalled everything according to plan, but of course as I went for a test ride I found it under the bench… so, now I’m trying to remove the crank again but it isn’t budging. That being said, they spin freely and there isn’t any play. Any tips on how to remove them again?