OK, so slewing seems to break the FocusCube communications somehow. When a meridian flip happens...  something breaks such that the Celestron CGX also breaks.
2021-05-03T11:01:24.129 ADT DEBG ][           org.kde.kstars.indi] - Pegasus FocusCube : "[DEBUG] RES <OK_FC:1.2:1:15.8:65935:0:1:0:0:0> "
[2021-05-03T11:01:24.511 ADT DEBG ][           org.kde.kstars.indi] - Pegasus FocusCube : "[DEBUG] CMD <0X41> "
[2021-05-03T11:01:24.512 ADT INFO ][           org.kde.kstars.indi] - Pegasus FocusCube :  "[ERROR] GetFocusParams error: Write Error: Input/output error. "
[2021-05-03T11:01:24.585 ADT INFO ][           org.kde.kstars.indi] - Celestron CGX :  "[ERROR] Serial write error: Write Error: Input/output error "
[2021-05-03T11:01:24.586 ADT INFO ][           org.kde.kstars.indi] - Celestron CGX :  "[ERROR] Failed to read RA/DEC values. "
The slew stops and it never recovers from this.

KStars 3.5.4 Beta  Build: 2021-05-02T06:04:05Z 
on Odroid-N2 ubuntu arm64-little_endian-lp64 Arch: "arm64  Kernel Type: "linux"  Kernel Version: "4.9.241-114"
full log file...
 

Hi jerry,

by looking at your log file log_10-49-59_2021-05-03.txt, everything looks fine till the meridian flip.
It is possible that after the meridian flip the USB cable or power cable connected to Pegasus FocusCube
had loose contact. I once had a similar problem with my focuscube. After properly and tight connecting USB and power cable the problem
was gone.

Thanks for that suggestion. I will test the hypothesis in (the) house.