Hi,

It is very unclear what you are doing with your ISR. While you are using the asm interrupt you cannot mix it up with basic code. That will overwrite your PBP system variables and you will get weird results. As for the 18F series if you are not using calls within your asm code. You can simply use retfie fast to restore your W,S and FSR without saving them. This is a single level shadow stack featured in the 18F series.