SSL Certificate Issue

Hi Good day.

Just want to ask help in regards with the issue that I encountered.

I have 2 ISP - ISP1 is set to be the mainlink which the distance is set to 1 and ISP2 distance is the backup link which the distance is set to 2.
Now, I’m trying to switch over it:
ISP2 - Distance = 1
ISP1 - Distance = 2

I successfully did that - But, I received an certificate issue with some sites. I attached a file for your references which I received on accessing Gdrive / Gmail.

Hope you could help me on my issue.

Thank you.
Error.PNG

Do you have hotspot enabled on any of the routers? Looks like something is intercepting your connections, or your routers are compromised and your DNS has been modified.