iOS Photon Cloud disconnect on old devices

We've got OnLeftRoom event on old devices after loading actual game scene (first person shooter level)
This occurs only on iPod Touch 4g (2010) and iPhone 4.
On newer devices this never happens.
We successfully tried to reduce memory consumption (memory consumption reduces significantly), but nothing changes.
How should we debug and fix this?
Are there any standard behaviours in Photon that can causes OnLeftRoom on old devices? (may be slow network module, or other timeouts, or something else)

Thank you!