Same project in two solutions throwing System.MissingMethodException in only one of the solutions

I've been stuck on this for weeks so I am completely at a loss at this point.

Basically I have solution A and solution B. Solution B is a recent branch of solution A with some added compilation symbols in a few project for changing screen dimensions. These two solutions also reference some of the same projects in the same directory as these are mostly utility/helper classes that will not be changed.

The project in question that is throwing the System.MissingMethodException is the same project for both solutions. It was not branched. It also does not contain any of these conditional symbols nor has it been modified since or before the branch.

The project in question deals with using the Microsoft Sync Framework to synchronize a local copy of a database with an SQL Server instance of the database. So of course, since we are talking about 1 project, the DLLs referenced for Microsoft Sync are the same across both solutions.

In solution A, the sync completes correctly. In solution B, when attempted to provision the client database, the System.MissingMethodException is thrown with the following details:

System.MissingMethodException
  HResult=0x80131513
  Message=Method not found: 'Microsoft.Synchronization.Data.DbSyncTableDescription Microsoft.Synchronization.Data.SqlServerCe.SqlCeSyncDescriptionBuilder.GetDescriptionForTable(System.String, System.Data.SqlServerCe.SqlCeConnection)'.
  Source=Windows Service Manager
  StackTrace:
   at ServiceManager.DataSynchronization.ProvisionClient() in DataSynchronization.cs:line 234
   at ServiceManager.Form1.DoFullSync() in Form1.cs:line 230

Perhaps the most curious part of this is that while debugging in Visual Studio I cannot step into the function that throws the error in solution B ( ProvisionClient() ). The moment I attempt to step in, that error is thrown. It is worth mentioning that the method that is allegedly missing is not called until 13 lines into the function.

In solution A I can step through the function until completion just fine. But, again, these are the same project

I am leaning toward this being a bug with Visual Studio 2019/the solution, but this is mostly just a hunch

Happy to provide any additional information that might be helpful.