Raspberry pi 4 Freezing if connected with internet

Hi,
I am running Ubuntu Mate 20.04.1 LTS, 64bit OS on my pi 4 4GB variant and it was running quite well till the last update, but after i updated the pi started hanging for at around every 10 minutes, during that time keyboard, mouse and display everything freezes. Then I noticed before freezing there is a pop up window of Task-Evolution (Some thing related to mail client I think), I tried unmarking all tick mark in the evolution settings but still the issue remains same. Also I came to know that it happens only if the pi is connected with internet.!

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I have tried changing power supply, and verified that the voltage is not dropping below 5.15V with a 6 Amp DC-DC converter, also the red indicator remains on and no yellow flash on screen when freezes.
Can anyone please find solution for this..