Comcast email intermittently not updating in Apple Mail

I have an interesting issue.

I have 2 iPhones and 2 iPads.

I will occasionally have an issue where my comcast email accounts will not update on one or two of my devices (almost never all of them) when connected to my home Comcast network via WiFi.  This only happens on my home network and only intermittently. If turn off WiFi on my phones the accounts will update via cellular and if I am having an issue with an iPad if I hotspot to my phone rather than connect to my network via WiFi it will also update.

i have no issue with my gmail, outlook, or yahoo email accounts updating when connected to my home WiFi, it is only an issue with my Comcast accounts. I find this strange, you would think a Comcast broadband network would, if anything, give preference to c9mcast accounts.

All settings on all devices are correct. They work fine 95% of the time, but the 5% that I have this issue it is very annoying, 

Does anyone have any ideas what might be going on?