2 springs are missing. The big one you have already mentioned which returns the key back to the 'neutral' position as it were which won't help.
The one causing you to have to hold the key over to get in, and the button up to get out, is a tiny little bugger which goes between the plates, also available from Skandix, or as I did, made one from a safety pin coil
https://www.skandix.de/en/spare-part...rlock/1038644/