Changing the number of iterations should automatically log you out on all devices. At least it did for me.

oh good, didn’t know if it would do that/force a cache invalidation for clients

It forced me out of all my logged in instances. I had to login to everything. With my master password and my 2nd factor.

That's important to realise, in case your (normal) second factor is a different Bitwarden device!

I didn't even think about this. My 2nd factor is through a different app, but if I'd been using BitWarden's TOTP I wonder if I would've been stuck.

A good reminder to also have printed (or something) OTPs accessible in a safe place in case you need them.