Hi @Lippy ,
Thanks for your patience.
I have checked internally and tried to create a server with both options enabled and it is possible:
make sure you have selected the correct Compute+Storage for HA i.e "Zone redundant high availability is not supported with the Burstable compute tier choice. If you would like to configure high availability, the compute tier will be upgraded to the General Purpose compute tier or you may choose a different compute tier"
Please retry and also try to change Region if it works.
If not, I would request you to raise support case so that your server could be diagnosed.
Thanks