Bad Character '[' after homing sometimes

As the title says, I am getting a bad character '[' used error twice after homing completes for the first time after starting LinuxCNC. It only happens sometimes. When I get the error and I started LinuxCNC from the terminal it shows this:

emc/task/emctask.cc 69: interp_error: Bad character '[' used
Bad character '[' used
emc/task/emctask.cc 69: interp_error: Bad character '[' used
Bad character '[' used

Since it only happens sometimes, I am not sure what to think or where to go from here. Any ideas? I have been unable to reliably reproduce it but it does happen often. I get it about 3 out of 10 times I start LinuxCNC.

Turns out this is related to an input that I have setup to trigger an E-Stop. When enabling the machine, the input toggles very quickly and causes an e-stop. Not sure what the bad character error is all about. Still trying to figure it out.