1.16.100.55 introduces a change listed as:

"Portal blocks placed with /setblock or /fill commands that are not part of a valid portal structure will only exist for 1 second before they are removed"

The change results in portals breaking in a ripple pattern, which generates increased amounts of lag by checking for valid conditions.

The portal breaking is also disparity with Java Edition, which breaks them all at once by doing the check beforehand

 
The problem appears to occur due to portal blocks now using pendingTicks rather than instant updates

How to reproduce:

1. Create a big nether portal
2. Break the nether portal

Expected results:

All of the portal blocks break simultaneously.

Actual results:

The portal blocks break one after another in a "ripple" pattern.