I've noticed lately that some of my comments are being edited - and not by me - to the point where questions asked of the OP are cut.
Why is that?
This is taken from How do comments work? on Meta.SE:
Users may edit their own comments any number of times for five minutes after they are first posted. Edited comments are marked with a little pencil icon, and a mouseover tooltip over that icon will provide a count of how many times the comment was edited, like this: Pencil icon
Moderators can edit any comment at any time. Moderator comment edits are logged and visible to other moderators, but no revision history is kept. Such edits will also show the pencil icon.
So the answer is that only you or a diamond moderator can edit a comment. Because no revision history is kept if you make a change other than it being visible how many time it's been edited (you can see examples on this question) no history is retained.
Moderator edits are logged presumably to stop a moderator with a vendetta being able to go off editing a user's comments to something inappropriate without leaving a trace for other moderators or the Stack Exchange team to investigate. For this particular case Dave Tweed has said he can't see any sign of any such edits, also the pencil icon isn't displayed.
My guess would be that you've either attempted to edit the comment or add an additional one that's gone off into orbit and never been received by the server. You can view the list of EE.SE moderators from this page and additionally most employees of Stack Exchange can perform the same functions (and more). A suspected comment edit seems a bit minor to worry about but if you did ever want to contact the latter for some reason there is a "contact us" button on the bottom of each page.