I upgraded the firmware to the latest EG12EAPAR01A11M4G version. And found my internet became much slower. Maybe it is a coincidence that ISP broke something, but the same ISP in the phone has a great connection.
During investigating I found the B7 channel is not working, but restarting the modem will always help. After restart, the internet became a bit faster (because B7 is live now).
I suspect the problem is firmware. But how I can downgrade it to test?
RouterOS v7.2.3
Chateau LTE12