MVAR_CLEAN on mutable list assertion failure

graphql-engine: internal error: MVAR_CLEAN on mutable list
    (GHC version 9.1.20201218 for x86_64_unknown_linux)
    Please report this as a GHC bug:  https://www.haskell.org/ghc/reportabug

This happens very occasionally when using the -debug RTS. The application makes extensive use of STM but I haven't managed to reliably reproduce it. Ticket here in case someone else ever runs into the issue.

To upload designs, you'll need to enable LFS and have an admin enable hashed storage. More information