SSDT Schema Compare doesn't work while a BULK INSERT is in progress
The OBJECTPROPERTY call requires a schema stability (Sch-S) lock, which is only incompatible with a schema modification (Sch-M) lock.

The BULK INSERT will take a Sch-M lock in some circumstances. These are listed in the "Table Locking and Logging During Bulk Import" section of Guidelines for Optimizing Bulk Import in Books Online:



If the destination table is clustered, you may find enabling trace flag 610 helps. Please read the whole series of those posts and the Data Loading Performance Guide and test thoroughly if you decide to go this route.

I have no idea why SSDT checks the IsEncrypted property for tables. I cannot imagine a scenario where that makes sense, but that's a question for the SSDT people.