Indeed, Mark, this is odd and should not happen. My best guess at this point is that something in the concrete environment is causing the file lock (e.g., source control making files read-only or the build may be downloading files from the source control and failing to replace them properly if they are read only). There is a "Get everything from source control when a project is opened" checkbox in the VS source control settings that has been reported to cause VS to fail to update the .designer files, so something similar may be happening.
I do hope that you will be able to continue working without issues because recreating the project is, indeed, feasible only in the start.
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