Some Post and Page Updates Don't Stick

Over the last couple of days, I’ve noticed that some posts and pages (seemingly arbitrarily) will not hold updates or changes. To try and solve this problem, I have:

– Disabled Revisions
– Set AutoSave to five minutes
– Cleared all browser cache
– Disabled all plugins
– I do not currently use a cache plugin

Here’s an example that might help illustrate the problem. The following is a page: https://americantwang.com/upcoming-country-album-release-schedule/

Each of the items on this page was in a list an unordered list. I was able to, section by section, remove the list tags. However, if I attempt to add a new line of text, the change absolutely will not stick.

Any ideas what I should do to troubleshoot this? Thanks, in advance, for your help.