Error: NP6: Invalid type message idx 16777214

Hello,

Has anyone come across this type of message? NP6: Invalid type message idx 16777214. I haven't been able to find any documentation that explains this message.

For context, I recently upgraded a HA pair of 500D to v5.6.2 and was having issue making the slave unit to synchronize with the master unit. A reboot of the slave unit fixed the HA issue but when it was booting up I notice this message to pop up constantly.