On a general note, I found a blog of a person who had Bluetooth problems with erratic mouse behavior on an iMac under El Capitan. His latest update was that some problems may be a result of a Handoff feature enabled in General preferences. His advice was to uncheck the “allow Handoff between this Mac and your iCloud devices” and restart the computer.
Will try to do it and see if this helps.

Last edited by macnerd10; 01/17/16 06:08 PM.

Alex
3.1 GHz 13" MacBook Pro 2015, 8 GB RAM, OS 10.11.2, Office 2011, TimeWarner Cable
2.8 GHz Xeon Mac Pro 2010, 16 GB RAM, OS 10.11.2, Office 2011, LAN