If that is the case, this won't be anything to do with Workstation Pro, it is the guest OS (Mint) which decides what to write and where. I've never used Mint, but can't imagine that is uses memory instead of disk space in the way that you describe.
Any issues at the host level with disk space would be unknown to Mint. Your 40Gb virtual disk is a set of files that grow in size, if there are issues with host disk space such that the files can't grow it would be the host OS complaining, not Mint.
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