FYI:

The SD card on nnrpi2 was full again causing issues, the log files in /var/log (kern.log & messages) were *huge* and filled with the same error many times a second

Oct  4 15:01:22 raspberrypi kernel: [1030048.603846]                                                                                                                                                                                                                                                                         
Oct  4 15:01:22 raspberrypi kernel: [1030048.607742] WARN::dwc_otg_handle_mode_mismatch_intr:68: Mode Mismatch Interrupt: currently in Host mode                                                                                                                                                                             
Oct  4 15:01:22 raspberrypi kernel: [1030048.607742]                                                                                                                                                                                                                                                                         
Oct  4 15:01:22 raspberrypi kernel: [1030048.667755] WARN::dwc_otg_handle_mode_mismatch_intr:68: Mode Mismatch Interrupt: currently in Host mode                                                                                                                                                                             
Oct  4 15:01:22 raspberrypi kernel: [1030048.667755]                                                                                                                                                                                                                                                                         
Oct  4 15:01:22 raspberrypi kernel: [1030048.667848] WARN::dwc_otg_handle_mode_mismatch_intr:68: Mode Mismatch Interrupt: currently in Host mode                                                                                                                                                                             
Oct  4 15:01:22 raspberrypi kernel: [1030048.667848]                                                                                                                                                                                                                                                                         
Oct  4 15:01:22 raspberrypi kernel: [1030048.731753] WARN::dwc_otg_handle_mode_mismatch_intr:68: Mode Mismatch Interrupt: currently in Host mode                                                                                                                                                                             
Oct  4 15:01:22 raspberrypi kernel: [1030048.731753]                                                                                             

A google issue showed that this was fixed in an update to Linux kernel, so I updated the kernel to the latest version.
now the message doesn't seem to appear so hopefully the pis won't break so rapidly.