It seems like a RAM usage problem. Your vCenter might be a bit short of RAM or there's something else going on in the background. Is your vCenter Windows based or is it the official appliance? Is anything unusual happening in the logs?
How much RAM is assigned to vCenter Server? How many ESXi hosts and VMs are in your environment?
Please refer to the following VMware Knowledge Base for VMware recommendations on RAM allocation in different infrastructures.
Please let me know if that helps.
Run the following command to output memory assigned to each of the services:
- cloudvm-ram-size -l
Increase the amount of memory assigned to the services by running the following command . I would recommend you to double the memory allocated
- cloudvm-ram-size -C XXXX vsphere-client
Restart the service that has been altered
- service vsphere-client restart
This should fix the issue for you .