AutoCorrect freaking out

Been using Word for 20 years and have never seen this - just started yesterday.

I can be typing for perhaps up to 20 minutes or so, but eventually my AutoCorrect starts to go crazy.  A good illustration is that I have an entry for 'gr' which becomes 'General Raymond'.  When I type 'grip', it becomes 'General Raymondip'.

It seems to sometimes reset when I close all Office apps, but it inevitably recurs, sometimes immediately and sometimes not for 20 minutes or so.

What the.....?    Thanks in advance...  Andrea