After mounting a network share in dolphin, entering "smb://path-to-network-folder" into the path selection toolbar, I lose access after a while. Then I can't even log into my windows laptop that is in the same samba domain. When logging in to my laptop I get the error: "The referenced account is currently locked out and may not be logged on to.". I need to wait for at least 30 minutes before I can log in again.

It seems to me that Dolphin is somehow keeping the connection to the samba share alive by passing login information at regular time intervals to the server. I suspect that it sends the wrong login information and that the server then decides to lock my account for 30 minutes.

Do you have any leads for me to debug this, or is this just a bug in Dolphin?

I think I can answer my own question here. The login name is "WORKGROUP\username" and I just used the login "username". I think that this username was stored in kwallet and that dolphin was trying to reconnect the samba share with this username. Probably after a few failed login attempts the user gets automatically blocked from its account for 30 minutes.
I deleted the old passwords from kwallet and re-entered and resaved the correct password and it didn't happen again sofar.