Verification builds:
1.5.3 | Nintendo Switch: Yes
1.6.0 | Nintendo Switch: Yes

Summary:
Infected villagers that are generated in Igloos will either die or disappear after converting from Legacy console editions to Bedrock.
 
Legacy console seeds used to test:
Seed: -538374388035947
Igloo #1: x 214 z 115
 
Seed: -3342585584230766181
Igloo #1: x 245 z 341
Repro Steps:

1. Create a world on Console edition using one of the seeds above
2. Ensure the world difficulty is set at Easy or above.
3. Travel to the igloo and verify that there is an infected villager in the basement of the igloo
4. Exit the world, and convert to Bedrock
5. Load the world in Bedrock and check whether the infected villager is present

Observed Results:
The infected villager disappears or dies during world conversion.  Sometimes rotten flesh can be seen on the ground in it's place.

Expected Results:
The world should convert over exactly, with mobs in place.

Screenshots/Videos attached: Yes

Notes:
Found whilst trying to test this bug: MCPE-36803