Socks...there are several insects that nibble on leaves.
Earwigs got to one of my Citrus last year. I had NO idea they were living in the soil since we haven't seen any the last 3-yrs.

Someone suggested waking in the early A.M. to see if EW's were on top of soil and/or leaves. The source woke early in the morn, and found EW's on leaves and soil of his plants. Other times of the day they were gone, hidden inside the soil.

In my case, after unpotting, there they were..Earwigs galore.
When plants are outside, 'and indoors,' many insects, 'including stingers,' make a home in and on our plants.

Have you inspected for other insect types? Toni

Toni, no I have not inspected but will do it. Thanks for the suggestion.

Toni, I inspected under the plant and in the nearby rocks on the ground and didn't see any earwigs. I removed the decimated leaves and noticed the newer leaves look pretty good, so maybe whatever it was moved on. Let's hope. Thanks.

Slugs and snails don't eat Begonias, which is another reason for me to love them (Begonias, that is - not molluscs...)

Socks, I too hope whatever moved on.
Once, a rabbit ate a Mimosa started from seed..first he/she nibbled, then one day, the entire plant was gone. lol.

Good luck, Toni

Hey Toni, if you see that rabbit again, let me know. I'll gladly pay his way down here!

Socks, your culprit could be European peppered moth caterpillar. If the munching has stopped, maybe you'll find a cocoon to destroy?

Purple, lol. Will do.

Actually, there's now a family of rabbits, squirrels, 'including one grey-furry type, eat my citrus fruit,' opposum, a zillion birds, 'they land on long-leaf plants,' raccoons, and an extra-ordinary number of ANTS!!!

You are welcome to all but the birds, lol.