After starting the SDL TMService Agent service, it stops after a few seconds. Attempting to restart it produces the same behaviour.

The first part of the Windows Event Viewer error shows the following:
 

Application: Sdl.TMService.Agent.exe
Framework Version: v4.0.30319
Description: The process was terminated due to an unhandled exception.
Exception Info: System.AccessViolationException
   at Icu.RuleBasedBreakIterator.SetText(System.String)
   at Sdl.Core.LanguageProcessing.ICU2.WordBoundaryFinder.FindBoundaries(System.String, Icu.BreakIterator)
   at Sdl.Core.LanguageProcessing.StandardWordBoundaryFinder.FindJaBoundaries(System.String)
   at Sdl.Core.LanguageProcessing.TokenizerHelper.getICUTokens(System.String, Sdl.LanguagePlatform.Core.SegmentRange, Sdl.LanguagePlatform.Core.SegmentRange, System.Globalization.CultureInfo)

Solution: Update to GroupShare 2017 SR1 CU10

The correct version of the DLL is present in GroupShare 2017 SR1 CU10. To update to this version, follow the instructions in this article.

Workaround: Replace old icu.net.dll file

If, for some reason, you are unable to update to CU10 at this time, then you can manually replace the affected DLL file.

WARNING: This should only be applied to a SDL Trados GroupShare 2017 SR1 CU9 installation. 

1. Download and extract the attached icu.net.dll file.
2. Navigate to C:\Program Files\SDL\SDL Server\TMService\
3. Rename icu.net.dll to icu.net.dll.old
4. Copy the icu.net.dll file you extracted in step 1 to C:\Program Files\SDL\SDL Server\TMService\
5. Reboot the server.

The icu.net.dll version 2.3.4.1 in C:\Program Files\SDL\SDL Server\TMService\ of GroupShare 2017 SR1 CU9 is out of date, and needs to be updated to version 2.5.4.0. This was resolved in the SDL Trados GroupShare 2017 SR1 Cumulative Update 10 release.