I am getting the same error but haven't updated the software past 1.5.5   
This build has been working great for quite some time and suddenly I am unable to calibrate guiding and get the error. 

GUIDE_RA error: 'mount or backlash problems

[2021-03-25T01:10:54.889 EDT DEBG ][     org.kde.kstars.ekos.guide] - Iteration  22  Direction: RA_INC_DIR  Duration:  2000  ms.
[2021-03-25T01:10:54.889 EDT INFO ][     org.kde.kstars.ekos.guide] - "Calibration rejected. Star drift is too short. Check for mount, cable, or backlash problems."

GOTO functionality works fine after a plate-solve.  Guiding from a saved backup works fine.   Here is a portion of the log which shows the final error.  Something is amiss in the mount itself as the same error occurs on a fresh SM 1.5.5 installation.

[2021-03-25T02:44:47.157 EDT DEBG ][     org.kde.kstars.ekos.guide] - Iteration # 17 : STAR  943.36 , 627.996
[2021-03-25T02:44:47.158 EDT DEBG ][     org.kde.kstars.ekos.guide] - Iteration  17  Direction: RA_DEC_DIR  Duration:  8000  ms.
[2021-03-25T02:44:47.159 EDT DEBG ][     org.kde.kstars.ekos.guide] - Star x pos is  7.02242  from original point.
[2021-03-25T02:44:55.335 EDT DEBG ][     org.kde.kstars.ekos.guide] - Capturing frame...
[2021-03-25T02:44:55.422 EDT DEBG ][     org.kde.kstars.ekos.align] - Mount motion finished.
[2021-03-25T02:44:57.039 EDT DEBG ][     org.kde.kstars.ekos.guide] - Received guide frame.
[2021-03-25T02:44:57.039 EDT DEBG ][     org.kde.kstars.ekos.guide] - Tracking Square  QRect(927,611 32x32)
[2021-03-25T02:44:57.054 EDT DEBG ][     org.kde.kstars.ekos.guide] - Iteration # 18 : STAR  943.085 , 627.331
[2021-03-25T02:44:57.054 EDT DEBG ][     org.kde.kstars.ekos.guide] - Iteration  18  Direction: RA_DEC_DIR  Duration:  8000  ms.
[2021-03-25T02:44:57.055 EDT DEBG ][     org.kde.kstars.ekos.guide] - Star x pos is  7.69011  from original point.
[2021-03-25T02:45:05.331 EDT DEBG ][     org.kde.kstars.ekos.guide] - Capturing frame...
[2021-03-25T02:45:05.366 EDT DEBG ][     org.kde.kstars.ekos.align] - Mount motion finished.
[2021-03-25T02:45:07.025 EDT DEBG ][     org.kde.kstars.ekos.guide] - Received guide frame.
[2021-03-25T02:45:07.025 EDT DEBG ][     org.kde.kstars.ekos.guide] - Tracking Square  QRect(927,611 32x32)
[2021-03-25T02:45:07.066 EDT DEBG ][     org.kde.kstars.ekos.guide] - Iteration # 19 : STAR  943.121 , 626.827
[2021-03-25T02:45:07.066 EDT DEBG ][     org.kde.kstars.ekos.guide] - Iteration  19  Direction: RA_DEC_DIR  Duration:  8000  ms.
[2021-03-25T02:45:07.067 EDT DEBG ][     org.kde.kstars.ekos.guide] - Star x pos is  8.19367  from original point.
[2021-03-25T02:45:15.302 EDT DEBG ][     org.kde.kstars.ekos.align] - Mount motion finished.
[2021-03-25T02:45:15.332 EDT DEBG ][     org.kde.kstars.ekos.guide] - Capturing frame...
[2021-03-25T02:45:17.213 EDT DEBG ][     org.kde.kstars.ekos.guide] - Received guide frame.
[2021-03-25T02:45:17.215 EDT DEBG ][     org.kde.kstars.ekos.guide] - Tracking Square  QRect(927,610 32x32)
[2021-03-25T02:45:17.288 EDT DEBG ][     org.kde.kstars.ekos.guide] - Iteration # 20 : STAR  942.703 , 626.345
[2021-03-25T02:45:17.288 EDT DEBG ][     org.kde.kstars.ekos.guide] - Iteration  20  Direction: RA_DEC_DIR  Duration:  8000  ms.
[2021-03-25T02:45:17.289 EDT DEBG ][     org.kde.kstars.ekos.guide] - Star x pos is  8.68095  from original point.
[2021-03-25T02:45:25.332 EDT DEBG ][     org.kde.kstars.ekos.guide] - Capturing frame...
[2021-03-25T02:45:25.550 EDT DEBG ][     org.kde.kstars.ekos.align] - Mount motion finished.
[2021-03-25T02:45:27.002 EDT DEBG ][     org.kde.kstars.ekos.guide] - Received guide frame.
[2021-03-25T02:45:27.002 EDT DEBG ][     org.kde.kstars.ekos.guide] - Tracking Square  QRect(926,610 32x32)
[2021-03-25T02:45:27.007 EDT DEBG ][     org.kde.kstars.ekos.guide] - Iteration # 21 : STAR  942.991 , 626.306
[2021-03-25T02:45:27.007 EDT DEBG ][     org.kde.kstars.ekos.guide] - Iteration  21  Direction: RA_DEC_DIR  Duration:  8000  ms.
[2021-03-25T02:45:27.008 EDT DEBG ][     org.kde.kstars.ekos.guide] - Star x pos is  8.7168  from original point.
[2021-03-25T02:45:27.015 EDT INFO ][     org.kde.kstars.ekos.guide] - "GUIDE_RA: Scope cannot reach the start point after 21 iterations. Possible mount or backlash problems..."


I am not sure where to look next and my problem isn't from updating to a more recent build.

Thanks IA for any suggestions

Steve

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