This didnt work either.
However, I found this thread here, where you were also contributing:
I entered some random username and pw to the network settings for windows shares. After that, I opened dolphin and navigated to the synology drive and I could finally enter the credentials. After that, the access to my synology drives via dolphin worked finally, but only for a short time!
However, after restarting dolphin again, the access doesnt work anymore (I am not asked for username and password anymore). It doesnt even work, if I again change the credentials in the network settings. It only worked for a short time…
I definitely think, the problem is the missing prompt for username and password. It never pops up in dolphin for me…