I have definitely encountered them in the last week or two.

I just did the following test. After the line above, I entered [asterisk] [space] (so I'm now in a bullet point), some text, then ctrl-4 to enter the LaTeX editor, entered some mathematics, hit enter to get out of the LaTeX editor, and pressed the space bar.

At that point, in the console I got this:

JavaScript error: https://www.lesswrong.com/js/bundle.js?hash=76bd6cfc5754522a5be764349f9bfc9d497abf9fe5ca29ce4eb640ef47e1976f, line 139: CKEditorError: H is null
Read more: https://ckeditor.com/docs/ckeditor5/latest/framework/guides/support/error-codes.html#error-H is null

That's the console window in which I started my browser, not the browser's Javascript console. In the Javascript console I got "Editor crashed", then Uncaught CKEditorError: H is null // Read more: ..." and a kinda-traceback, then "Editor was restarted". But apparently once restarted it's a bit confused about its internal state. Here's the kinda-traceback:

init liststyleediting.js:215
fire emittermixin.js:209
_convertItem upcastdispatcher.js:249
convert upcastdispatcher.js:207
toModel datacontroller.js:414
_runPendingChanges model.js:830
change model.js:175
toModel datacontroller.js:413
_handleContainerChildrenMutations injecttypingmutationshandling.js:109
handle injecttypingmutationshandling.js:64
init injecttypingmutationshandling.js:22
fire emittermixin.js:209
_onMutations mutationobserver.js:249
o ckeditorerror.js:61
rethrowUnexpectedError ckeditorerror.js:117
fire emittermixin.js:244
_convertItem upcastdispatcher.js:249
convert upcastdispatcher.js:207
toModel datacontroller.js:414
_runPendingChanges model.js:830
change model.js:175
toModel datacontroller.js:413
_handleContainerChildrenMutations injecttypingmutationshandling.js:109
handle injecttypingmutationshandling.js:64
init injecttypingmutationshandling.js:22
fire emittermixin.js:209
_onMutations mutationobserver.js:249
_onMutations self-hosted:1173

(It's actually presented in table form, function names on the left, filenames and line numbers on the right.)

I get these all the time.