Unfortunalty, I believe it's because only the plain text content control is supported. I tried a number of manipulations on the Flow side, but because the text is normal until it hits the Word doc, everything looks fine as far as Flow knows.
I had to move on to other things, so like you I am just using nested replaces to remove the unsupported characters and replacing '&' with 'and'. Not the most ideal or professional looking option, but until the connector is updated to support rich text content controls there doesn't appear to be anything else that can be done.
If you end up figuring something out, I would love to hear about it. I'll update this thread is well if I end up coming across anything.
