Spell Checking Unavailable in SharePoint 2016/Office Online Server

[Gary Schultz]

Have SharePoint 2016 Enterprise installed with Office Online Server. Spell check stopped working, users receive the message "Spell Checking Unavailable." This worked at one time and I'm not sure when it broke, but it seems likely an update broke it. 

[#2]

Is this feature still activated?

http://expertsharepoint.blogspot.com/2014/02/the-spelling-check-cannot-be-completed.html

[#3]

Yes, the feature is activated. Spell check worked at one time, and simply stopped working. It is another example of something that worked in SharePoint 2016, then simply stopped working. Much like images placed in Notebooks in OneNote 2016 that were visible when viewed in browser, but now are no longer visible in browser. 

[#4]

@Gary Schultz Hi Gary

Did you get it to work again? I'm facing same problem on SP2019.

Regards Thomas