On validator registration, committee drops entire slot

[Roy-blox]

Describe the bug
While registering new validators we have a mechanism to not attest on registration epoch + 1 to avoid slashing attacks, in post fork we see that the registration slot drops completely instead of only dropping the newly added validators.

To Reproduce
Steps to reproduce the behavior:

1. Have a post fork cluster with some validators on it
2. Bulk register some validators

Expected behavior
Only new validators will not attest on registration epoch while the rest attest as expected

Actual behavior
All validators that were supposed to attest on registration slots failed.

Node (please complete the following information):

• Operator Version: v2.0.0 - Post-fork