Then its likely you’re looking at some sort of conflict. A few things to try:
1. Press CTRL-F5 key combination while viewing the thread – this will do a hard refresh of your browser cache.
2. Turn off COMBINED CACHING option under FORUM->OPTIONS->GLOBAL SETTINGS.
3. Open up your browser console and see if there are any javascript errors being shown in there.
4. Switch your WordPress theme to one of the core 2017/18/19 theme, clear your caches (if you or your host have any turned on) and see if the text shows up.
5. Go to FORUM->TOOLBOX->ERROR LOG and clear the log. Then try viewing the forum again and see if any new errors show up in that log.
6. Check your WordPress debug.log file to see if there are any errors being thrown in there. (You might need to turn on your WordPress debug flags first).
You can do all of these things individually – they’re not dependent on each other. I just listed them in the order of easiest to hardest.
Thanks.
PS: You might want to verify that your PHP version is 5.6.30 or later. Also, what browser are you testing in? I assume its something mainstream like Chrome on Windows?