Hello, I have the same problem. I undesrtood that the problem might be connected to the firmware version that you have on your printer. I updated my X1C to the latest version 01.07.02.00. It worked fine for few days than yestarday the printer got offline. Thare is a topic related to it: Update to firmware version 01.07.00.00 and LAN only mode
I partially solved the problem switching to LAN connection. Now I can control the printer using bambu studio even if I can’t use the bambu handy app. In this video you can find usefull informatoin: https://youtu.be/TCLN7UoZa6Y?si=zE8LLrh7JIQ8o7AV
I think we have to wait until the next frimware update wil be produced or contacting Bambulab in order to downgrade the printer to the previous firmware in my case.