This happened because AWS DocumentDB is only mongo 4.0 compatible and I was trying to restore from mongo 4.2, to solve this I just used AWS DMS as it was free, process is simple and there are many tutorials available from AWS and as well as other people on youtube
An answer to this question was provided on the AWS Developer Forums thread to which it was originally posted.
RDS PostgreSQL (as of the versions available in April 2018) doesn't always recover after restart; however, if the RDS instance does not shutdown within an unspecified timeout, RDS will force terminate the instance, requiring PostgreSQL to ...
(Disclaimer: I work at QuasarDB)
Because you are using the newer gp3 EBS volume types, and you are reporting a system-wide instability of the system (rather than just the QuasarDB process), I believe this is related to the EBS volume types, rather than something related to QuasarDB.
We have observed stability issues with gp3 volumes under high pressure ...