Hello Oleh Yemelianov,
I used to experience this as well, i'm not sure if we both have the similar issue, but in my case it was a heap size issue for the vSphere H5 Webclient, login in on the console of the VCSA, and run "vimtop" Look for: vSphere H5 Web Client 1112 0.00 0 13.99 2665.58 9691.71
Use the following command to check the current value:
cloudvm-ram-size -l
look for: vsphere-ui
probably it is very low, you can increase this to the range you see in "vimtop"
This example, set the heapsize to 4GB:
cloudvm-ram-size -C 4096 vsphere-ui
then
Restart the service that has been altered, in this example vsphere-ui:
service-control --stop vsphere-ui;service-control --start vsphere-ui;
Hope this will help => the source KB: https://knowledge.broadcom.com/external/article?legacyId=2150757