It looks like the multiple client flag gets incorrectly reset again after login with another client (in my case Skype for Business Android app):
(14:49:15) sipe: sipe_ocs2007_process_roaming_self: single client detected
(14:49:36) sipe: sipe_ocs2007_process_roaming_self: multiple clients detected (2)
(14:49:36) sipe: sipe_ocs2007_process_roaming_self: single client detected
(14:49:40) sipe: sipe_ocs2007_process_roaming_self: multiple clients detected (2)
(14:49:40) sipe: sipe_ocs2007_process_roaming_self: single client detected
(14:49:42) sipe: sipe_ocs2007_process_roaming_self: single client detected
Forums: Multiple client behavior
Release Notes: 2017/06/pidgin-sipe-release-1221
Looks like the server can send roaming self NOTIFY without device entries. We shouln't update the single/multiple client flag in that case.
Fixed in git commit aad8bf6