Ah, you have my apologies @Keith_Glover1, I had your core device mixed up. My above reply won’t apply to your NUC in this situation.
Roon has used SMB2.1 for quite some time, it was one of the first added since the protocol integration became possible in the software.
The primary issue is that the Sooloos device is still using SMB1 which is quite outdated. Are you able to test another device that can host SMB sharing, and add a small portion of your local library to it? I would also see if there’s an option to add additional SMB sharing protocols to the MC200.