GGSN - Code 211 - All dynamic addresses are occupied

Hi Experts,
Any idea why there would be cause code 211 sent by GGSN IN create PDP response - ALL DYNAMIC ADDRESS ARE OCCUPIED?

IP Pool congestion.

This site can also be useful for GTP Cause Codes.

https://www.developingsolutions.com/reference-guides/gtp-cause-codes/

211 (GTPv1)
All dynamic PDP addresses are occupied
Indicates that the GSN does not have a free dynamic PDP address to allocate any longer.

Checked: IP Pool, DHCP, everything ok.
SGW reselection is not working when cause #84 received from ggsn.

Got this from a friend:
Each APN has IP pool for it inside GGSN.
For example IMS APN has 100 IPs.
If 100 IPs assigned, then new users will get error code 211.