Teensy LC ttyACM not working, perhaps udev or hotplug issue

Hi,

I have a Teensy LC connected to my Openwrt router via USB and I am reading serial data from ttyACM0. However after a few seconds of receiving data it stops and the following error messages show in dmesg

[   91.457149] random: crng init done
[  239.642080] usb 1-1: clear tt 1 (9044) error -71
[  239.749078] usb 1-1: clear tt 1 (9044) error -71
[  239.859080] usb 1-1: clear tt 1 (9044) error -71
[  239.969077] usb 1-1: clear tt 1 (9044) error -71
[  240.079078] usb 1-1: clear tt 1 (9044) error -71
[  240.188076] usb 1-1: clear tt 1 (9044) error -71
[  262.391077] usb 1-1: clear tt 1 (1043) error -71
[  262.499080] usb 1-1: clear tt 1 (1043) error -71
[  268.822094] usb 1-1: clear tt 1 (1043) error -71
[  268.938113] usb 1-1: clear tt 1 (1043) error -71
[  269.049079] usb 1-1: clear tt 1 (1043) error -71
[  269.159080] usb 1-1: clear tt 1 (1043) error -71
[  269.300078] usb 1-1: clear tt 1 (1043) error -71
[  269.409087] usb 1-1: clear tt 1 (1043) error -71
[  269.519078] usb 1-1: clear tt 1 (1043) error -71
[  269.629080] usb 1-1: clear tt 1 (1043) error -71
[  269.739081] usb 1-1: clear tt 1 (1043) error -71
[  269.889080] usb 1-1: clear tt 1 (1043) error -71
[  465.903181] cdc_acm 1-1.2:1.0: failed to set dtr/rts
[  465.976082] usb 1-1: clear tt 1 (0040) error -71
[  466.057169] usb 1-1: clear tt 1 (9044) error -71
[  466.137174] usb 1-1: clear tt 1 (0040) error -71
[  466.227198] usb 1-1: clear tt 1 (9044) error -71
[  466.337176] usb 1-1: clear tt 1 (1043) error -71
[  466.410514] usb 1-1: clear tt 1 (9044) error -71
[  466.497171] usb 1-1: clear tt 1 (1043) error -71
[  466.567130] usb 1-1: clear tt 1 (9044) error -71
[  466.678081] usb 1-1: clear tt 1 (9044) error -71
[  466.789080] usb 1-1: clear tt 1 (9044) error -71
[  466.899088] usb 1-1: clear tt 1 (9044) error -71
[  467.009079] usb 1-1: clear tt 1 (9044) error -71
[  467.119081] usb 1-1: clear tt 1 (9044) error -71
[  467.242080] usb 1-1: clear tt 1 (9044) error -71
[  467.349074] usb 1-1: clear tt 1 (9044) error -71
[  467.459061] usb 1-1: clear tt 1 (9044) error -71
[  467.615083] usb 1-1: clear tt 1 (9044) error -71
[  467.728074] usb 1-1: clear tt 1 (9044) error -71
[  467.839081] usb 1-1: clear tt 1 (9044) error -71
[  467.949078] usb 1-1: clear tt 1 (9044) error -71

I've read that the Teensy boards need a udev rule but Openwrt doesn't have udev (only hotplug), so assuming this is the issue how do I get around it? Any help would be much appreciated!