Questions on Sceliphron caementarium Nesting Behavior

[eumenes]

A couple of Sceliphron caementarium recently built nests above my front door, and I'm curious about some of the behavior I've seen.

In the first nest, typical emergence holes appeared after a couple of weeks, but some of those cells were then re-sealed within a day or so, presumably by the nest owner. What might the purpose of re-sealing the cells be?

Also, after the first nest was completed (by "Wasp A"), another S. caementarium ("Wasp B") completed a nest about six inches away. Wasp B then started occasionally adding mud to and frequently resting on Wasp A's nest, even though Wasp A was still spending a lot of time there. Sometimes both wasps were on Wasp A's nest, and when they were, they usually attacked each other (with their mandibles). Wasp A was usually the one to retreat from these fights and fly away.

Is Wasp B's behavior (adding mud to another individual's nest and trying to drive the nest owner away) common for this species?