Thank you for the update, We would like to inform you that the KB that you are referring to is for ESXI 4.X.
There is not such known issues with ESXI 6.5, For Powering ON Virtual Machine with a Specific Reservation.
If you would like to reserve the complete available memory on the Host.
First you would have to increase the Memory Allocated on the Resource Pool.
Once the Resource pool has been allocated with the required Memory, then you would be able to Reserve or allocate the memory on the Virtual Machine.