New minor, but annoying problem. Can anyone help?

When a new email arrives, I have my Settings/Notifications set to flash the light for "no limit" in order to alert me. Unfortunately, the amber light flashes for only a minute or two, then goes back to flashing green. A minute or two isn't even an option.

My missed calls and voicemails are also configured to flash the light for no limit, and that works OK. Just the email light alert is giving me trouble.

Thank you.

Edited to add: I just changed the alert function to 60 mins., the max, yet it still just flashes for a minute or two.