WAF / ASM : Referer: android-app://com.google.android.gm - Evasion Technique detected

Seems to happen for more people and was sort of an attack at some time, but then mainly for trailing slashes, is that also in your case?

I think what mainly matters is if that breaks funtionality on your website? Do you see traffic which feels legimate that triggers this alert? Because if not I would certainly not disable the alert. If it seems to be needed I would look into only disabling it in the cases needed.