HighSierra: reads/writes fail, applications freeze until restart

In the last 2 months, all of a sudden, one of my 2 Macs running Mac OS X High Sierra starts generating file system write errors if left on for more than 4-6 hours. The immediate error message that shows this state has triggered is coming from Visual BASIC (Spyder Elite 5 uses this):

Location: /Users/realsoftware/BuildSlave/StableCarbon/build/REALbasic/REALbasic/Xcode/... /.../Common/ClassLib.RuntimeThread.cpp: 2662

Failure Condition: mutex ->mLockFile

Failure Message:

Please report what caused this error along with all of the details

This error message appears to be an indicator when the condition happens, not the cause. Any other applications running that use my APFS startup volume freeze, fail to write, fail to read data (some operate if they are unlicensed).

A simple restart fixes the problem for the next 4-6 hours.

I've seen others post this problem but no obvious answers. What I've tried:

- Look at Activity Monitor for unusual memory usage (system is not out of memory)

- Disk Utility -> First Aid when the problem occurs
(High Sierra lets you do this live on the startup volume, no errors found)

- OS X re-install