Messages brings macOS to its knees with soagent and callservicesd
As the issue is related to the spell checking feature I would suggest you to reset text replacement.

You can erase (or save, if learnt spelling matters for you) all files in:

~/Library/Spelling


Do not forget to kill the spell process (something like AppleSpell) but remember to quit Message.app before doing so.

Also try to delete all the entries (if you ever added one) by hitting minus sign in Settings.app > Keyboard > Text Replacement

Note that your problem seems to be closely related to this one (as pointed out in some answers). To sum up the solutions discussed:


Navigate to ~/Library/Containers/com.apple.soagent/Data/Library/Preferences and delete (Drag to Trash) the com.apple.soagent.plist and then Restart the computer.
The second solution was pointed out by Everett.