Why do my capsules start flipping every time I go EVA in space?

[Neil Kermstrong]

Every time I leave my capsule to do something, like collect science from another vessel or just make an eva report, the capsule suddenly starts flipping and it makes it impossible to enter it again.

Rn I had this problem, so I loaded my previous quicksave to discover that save was from the previous launch

[Spricigo]

You may briefly hit time warp to stop all rotation. 

If mods are an option for you there is easyboard.

[Geonovast]

The capsule is doing this if there's nothing left on board to control it - either a kerbal or a probe core.  With no control left on it, SAS, and therefor the reaction wheels, are disabled.  When your kerbal pushes off the  pod, it puts a force on the pod that is not aligned with the center of mass, which causes it to spin.  So the first fix is to stick a probe core on board that will keep SAS running.

The second fix is a bit of a trick.  If you time warp, all motion stops as the game stops calculating physics during normal time warp.  If you tap > and then tap / to time warp for just a second, your pod will stop spinning.

[N_Danger]

You can also use a capsule that takes more then one passenger and take 2 pilots.

[Spricigo]

On 10/24/2020 at 2:17 PM, N_Danger said:

You can also use a capsule that takes more then one passenger and take 2 pilots.

Yes, but I'd rather bring a pilot and a scientist.

[Superfluous J]

If it happens while you're still on the ladder, your Kerbal may be clipping into the ship. Physics tries to move them apart, so it moves the ship away from the Kerbal. The Kerbal follows the ship because it's on the ladder, which causes the clipping to remain.

The only way to fix this is to make sure the Kerbal doesn't clip into the ship. None of the stock pods would do this on their own, but all of them could do it if you add parts in the right (wrong?) places. Making History's Eagle replica pod is particularly susceptible to this, but putting large things on the top of a Mk1 pod can even do it.