This is a Linux feature, and not unique to BBB.
When Linux sees something it does not like with respect to file system handling or I/O, it will convert that file system to RO, to prevent further damage.
Research "Linux making file system Read Only" or something similar.
You are likely violating something with respect to permissions, or making I/O errors.
To clear the "Read Only" protected status, you will need to do something like
Google is your friend.
--- Graham
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