When HTML5service.exe is not anymore running and accordingly not displayed in the task list or service not anymore listed by AdminTool GUI as started even if it was running fine before then most likely Java VM has crashed with "out of memory" error. In such case Java usually creates crash dump file in *\Clients\webserver\hs_err_pid*****.log with extended information about occured crash.

There are two options how to solve that problem, either install more physical RAM or try to force Java to run in extreme mode. In this mode Java VM will reserve more memory and won't give the memory back to system but reuse it for future tasks. To do that follow walkthrough below.

1. stop HTML5 server in AdminTool GUI firstly

2. Uninstall all Java versions you find.
Moreover, after uninstalling remove two folders with all subfolders if existing "C:\Program Files\Java\" and "C:\Program Files (x86)\Java\"

3. then download and install latest Java JDK version from here Java JDK download
As example: Windows x64 206.76 MB jdk-8u162-windows-x64.exe or newer version if available.
Remember, you need exactly 64bit version by 64bit Windows (never use 32bit version on 64bit Windows)
JDK version is needed because it is able to use extra specific options/switches unlike usual JRE edition.

4. logoff all users except your self, not just disconnect but logoff each user completely! THAT IS MANDATORY!

5. now restart in AdminTool GUI the HTML5 webservice, for now that is needed to force TSPlus to write new Java path into starting batch file runwebserver.bat

6. now locate *\webserver\runwebserver.bat and open/edit it with Notepad.

7. since you should have already restarted HTML5 server in AdminTool GUI in step 5. then now go sure that the path to Java directory in the file *\webserver\runwebserver.bat refers to REALLY existing path for freshly installed Java JDK version, you should uncheck Attribute: Read-Only from file runwebserver.bat if it was set before HTML5 restart.
So finally inside that file you should get something like following
@"C:\Program Files\Java\jdk1.8.0_162\bin\HTML5service.exe" -Djdk.tls.ephemeralDHKeySize=matched -Djdk.tls.rejectClientInitiatedRenegotiation=true -Dorg.jboss.netty.epollBugWorkaround=true -XX:+UseG1GC -XX:+AggressiveOpts -XX:MinHeapFreeRatio=10 -XX:MaxHeapFreeRatio=10 -cp "%~dp0httpwebs.jar" -Duser.dir="C:\\Program Files (x86)\\TSplus\\Clients\\www" com.jwts.socketjw.NSIOServer 80 443 secret secret -81 22 3389 >weblog.txt

8. now to the line above add two new parameters -server and -XX:+AggressiveHeap
it should look something like
@"****\HTML5service.exe" -server -XX:+AggressiveHeap -Djdk.tls.ephemer*****
and additionally to that REMOVE three options -XX:MinHeapFreeRatio=10 and -XX:MaxHeapFreeRatio=10 and -XX:+UseG1GC
So you will avoid the situation that Java returns freed memory back to system.
So finally you should get the batch file approximatelly looking like that
@"C:\Program Files\Java\jdk1.8.0_162\bin\HTML5service.exe" -server -XX:+AggressiveHeap -Djdk.tls.ephemeralDHKeySize=matched -Djdk.tls.rejectClientInitiatedRenegotiation=true -Dorg.jboss.netty.epollBugWorkaround=true -XX:+AggressiveOpts -cp "%~dp0httpwebs.jar" -Duser.dir="C:\\Program Files (x86)\\TSplus\\Clients\\www" com.jwts.socketjw.NSIOServer 80 443 secret secret -81 22 3389 >weblog.txt
IMPORTANT: do not just copy/paste entire line from this walkthrough since you could have different Java path or different ports inside your original line, so make changes on your original line!

9. IMPORTANT: set on this changed file runwebserver.bat > Attribute: Read-Only, so that this file can't be overwritten anymore! If you forget to finish that step then all your changes will be reverted to default values by AdminTool GUI 

10. now final step, start(restart) HTML5 server in AdminTool GUI again.

By next opportunity install more physical RAM else your Windows programs will suffer due lack of the physical memory!