Looking more closely at the device type it is different from other tty devices.
It is the only device with those major and minor numbers but that may not be an issue.
0 crw--w---- 1 root tty 240, 0 Oct 16 05:58 /dev/ttyGS0
This is interesting also.
It appears to be a character device though.
And some more info:
File: /dev/ttyACM0
Size: 0 Blocks: 0 IO Block: 4096 character special file
Device: 6h/6d Inode: 14407 Links: 1 Device type: a6,0
Access: (0660/crw-rw----) Uid: ( 0/ root) Gid: ( 20/ dialout)
Access: 2019-10-16 05:58:29.736796001 +0000
Modify: 2019-10-16 05:58:29.736796001 +0000
Change: 2019-10-16 05:58:29.736796001 +0000
Birth: -