Welcome aboard!
Someone who knows what they are talking about will be along presently, but ...
Assuming the oil is topped up correctly, it's possibly a dicky oil pressure sensor. The OPS can throw up some odd readings if it's faulty.
Failing that, I've heard tell that the instrument board of the 999 can be a bit flaky, although mine's been fine (touch wood).
Suggest you get the vendor to replace the OPS and monitor. Good luck!