The original error seems to be related to https://github.com/MarlinFirmware/Marlin/issues/36... Using Marlin 1.1.0 RC8 with MC 1.6.1 I also have this issue even if as it looks Marlin and MC seem to be able to deal with it. If it happens it will cause a tiny delay that may be the reason for the bridge issue.
With MC1.6.2 the M110 N1 seems to cause the problem. Using a terminal and replaying the commands manually M110 acts strange:
M110 N0
ok
N1 M105*38
Error:Line Number is not Last Line Number+1, Last Line: 2
Resend: 3
ok
echo:Unknown command: "ok"
ok
Error:Line Number is not Last Line Number+1, Last Line: 2
Resend: 3
ok
N0 M110 N1*124
ok
N2 M115*36
FIRMWARE_NAME:Marlin 1.1.0-RC8 (Github) SOURCE_CODE_URL:https://github.com/MarlinFirmware/Marlin PROTOCOL_VERSION:1.0 MACHINE_TYPE:ANYCUBIC EXTRUDER_COUNT:1 UUID:8112eb85-d15b-460e-8089-f83b108660bf
ok
N1 M105*38
Error:Line Number is not Last Line Number+1, Last Line: 2
Resend: 3
ok
N0 M110 N1*124
ok
N1 M105*38
Error:Line Number is not Last Line Number+1, Last Line: 1
Resend: 2
ok
N25 M105*16
Error:Line Number is not Last Line Number+1, Last Line: 1
Resend: 2
ok
M110 N0
ok
N1 M105*38
Error:Line Number is not Last Line Number+1, Last Line: 1
Resend: 2
ok
From the Marlin documentation, the short form w/o line number should work without checksum, but in fact, does not. So I would assume the M110 command to be broken, maybe somewhere on the road to or from RC7.
Guess a good suggestion for Mattercontrol 1.6.2 might be to revert to the communication as it was in 1.6.1 and maybe reduce the M105 frequency a bit to relax communications.