After transferring a call, the next call has a ringing sound

We have this issue. Any time a user transfers an external phone call, the next time they receive a call they hear ringing.

Does anyone have some suggestion to try to fix this issue.

It does not happen on all phones, but on most.

We’ve check phone and extension settings…

We are using Freepbx version 2.8.1.4.

The phones are Polycom model IP 550’s.