Api problems with "Internal Server Error"

I am trying to use the api to upload several thousand issues from an internal system. Whilst I can post individual issues and everything works, if I try and post more than one at a time (multiple requests) gitlab throws out an {500 - internal system error }.

Is there a flag / setting anywhere that may be creating this behaviour ? I obviously don’t want to wait for each issue to be created through the api before creating the next one