This is just a heads-up at present. I'm still investigating what is happening.
Using Firefox 66.0.5 and Joomla 3.9.6 and SP Pagebuilder Pro, I have a text box that I can type into, and it used to work fine, but with the latest version of JCE, each character I type is erased as I type it. If I go into the code editor and type some text, it lets me, but when I switch back to the edtor, the text I typed is all gone.
Switching to TinyMCE, I find there is no such problem.
I am running with Firefox in Safe Mode (addons disabled) to avoid the complications of any add-ons.
I'll update this post with any further findings.
Brian