I'm sorry, but I guess my post was a bit incomprehensible.
How I use MC:
Running MC19 on a HTPC connected to a TV and a DAC. I controll MC typically with a Harmony Remote Control within the theater view and sometimes with my tablet with Gizmo when my TV is off.
All my data is stored on local SSD on my HTPC! There are no external drives or any NAS.
When I want to maintain some metadata e.g. tagging some music files, I use a normal Desktop-PC that runs another local instance of MC. From here, I use the functionality "Load Library" to connect my desktop pc with the library from the HTPC.
So there are 2 situations where I do a remote connection:
1) With a tablet using Gizmo, to control my HTPC
2) With a desktop pc, running a local instance of MC, that connects to the library of my HTPC
The problematic case:
Typically my HTPC is in hibernation mode when not used. I wake it up, either with a WOL tool or with my harmony remote control.
After awaking the HTPC, MC is running without any problems. I can play music and control it with my harmony remote.
Now, if I want to do a remote connection as described in situation 1) and 2) I get a connection error.
As I described in my first post, the only workaround I found, is to restart MC on my HTPC or just wait for some time.
Hope the problem is now a bit more clear. Thanks!