Zebra QLN320 does not see bluetooth ios apple

Hey. I have many zebra QLN 320 printers with bluetooth. We work with them every day; they are connected to an ipad tablet. Many printers have stopped working, our ipad do not see them on bluetooth. Periodically and to this day the printer stop working. They used to work, MFI is present in them, but not a single ipad tablet with different ios does not see them. On one of the printers, I sent a command

! U1 getvar "bluetooth"

! U1 do "bluetooth.clear_bonding_cache"

Result

bluetooth

bluetooth.discoverable: on, Choices: on, off

bluetooth.friendly_name: Optom3

bluetooth.version: 4.2.1

bluetooth.date: 09/10/2012

bluetooth.local_name: Optomoll-3

bluetooth.address: AC: 3F: A4: 42: 5D: AF

bluetooth.bluetooth_pin: *

bluetooth.short_address: AC3FA4425DAF

Firmware on priter 68.19.7Z

I updated many of the printers to the latest firmware V68.20.10Z, but this did not help, I also reset the cache, reset the settings, but it does not help. In Russia, no service center can understand the problem, they say the technical part is all right.