I have the same problem but interestingly this problem seems to be more complicateted. I have two NAS in my network. My phone can connect to both with SMB v2 but my tablet can only connect to one of them with SMB v2 for the other one I have to use SMB v1. A different file explorer on my tablet connects to both with SMB v2. So my guess the problem is within the solid explorer!
I have the same problem but interestingly this problem seems to be more complicateted. I have two NAS in my network. My phone can connect to both with SMB v2 but my tablet can only connect to one of them with SMB v2 for the other one I have to use SMB v1. A different file explorer on my tablet connects to both with SMB v2. So my guess the problem is within the solid explorer!