Letters disappearing when typing

Hi all,

An odd one, this.

When typing for work, I have to use abbreviations. One of them if the letter "P" and "O" next to each other, as PO. However, when I type these letters into my Mac, they disappear! It's almost like they are being autocorrected away to blank.

I do the majority of my typing in Word, and it is not a shortcut in there, as a) I have checked the settings, and b) it happens across all apps (Safari, Outlook, Notepad etc) suggesting to me that it is an issue with the OS. I have checked my keyboard shortcuts in there too, but there is nothing to indicate that this should happen.

It happens if I type in upper or lower case, or a combination. In order to write the offending letters at the start of this post, I had to type them with a third letter, carry on typing and then return an delete the third letter. It seem the action only occurs when I press space or return after the PO.

Very odd.

I've searched the communities and cannot find an answer. Sorry if I have missed it.

Any guidance gratefully received.

I'm running Mojave 10.14 on a 2016 MacBook Pro.

Thanks for reading!!