When using NX Client for Windows in a Linux session and error below is reported:

One or more fonts that are in use by the session are missing

in many cases it is enough to install the add-on fonts on the Windows machine to solve the problem of missing fonts.

By extracting the logs and looking for the line "Info: Reconnection failed: Couldn't restore the font ..." you will see which font is missing. Installing it should allow you to connect to the suspended sessions, previously not possible.