Never format a card on a computer and stick it back into the camera. I would say just put another card in and remember to format it in camera only. Another thing, don't delete images off your card when in camera.
I always deleted photos both ways...
Not a good idea. Just as the PC will mess up the file allocation table (fat table), deleting files in the card from the camera can do the same. Think of it this way, if you formatted your card in camera, bits of the images are still allocated inside, hence you can actually perform a rescue and recover them even if you formatted. The camera literally will save the information of the images until you start shooting again and that info will be over written. Example: your on a shoot and take 20 images, downloaded them on a computer, put the card back in the camera, and format it...there is data from those 20 images still on it that you can recover using software on a computer. It will still be there until you have taken 20 more images.
When you format the card in a computer, it is much more sophisticated and handles that fat table differently. The camera handles that fat table in a much less sophisticated way. That's why your camera didn't know what to do.
I used to do data recovery and it is much more complex than I am stating, just trying to simplify it for you. I once had a woman bring me her computer, she wanted to find out what her husband was doing on the PC, she didn't think I could find out because he cleared his history and deleted files. Um, I recovered all of his history going 6 months back, plus recovered documents and images.
I recently recovered a micro sd card in a phone for a friend. She was deleting her images on her phone and it messed up the fat table on the card. She was devastated because all her images were on there and she didn't back it up on line. I recovered all her images ( well over 2000). We then put a new card in the phone, formatted it in phone, and set up a Google account to back it up moving forward. I also uploaded all her old images on Google photos. She will never have that issue again.