I asked around a bit and no one has come across this symbols. One committee member thinks it is a print error!
The suggestion I was given to pass along was:
If the transcriber uses a transcriber-defined symbol because they can't just substitute an arrow and "fix" the print error, I believe it should be listed on the Special Symbols page (or in a transcriber's note in the body if the mystery symbol only occurs on that page) something like:
⠨⠿⠹ First transcriber-defined symbol, used to indicate a spelling change in stem-changing verbs
Write back if you were given other interesting suggestions!