I have a Galaxy S6 Edge+ phone and since updated at Android 6.0.1 Marshmallow, I’ve got some problems.
My problems started in using Facebook Messenger and Whatsapp, but not only. The Wi-Fi connection fluctuations was also present with packet loss every time.
On 3G/4G these apps mentioned above keep losing connection, especially in video or voice calls.
After about 2 weeks, I found the problem and happily with solution:
On other android versions (4.x and 5.x) I’ve used the “Power Saving” mode without any problems related to apps functionality, but from the Android 6, power saving algorithms seems to be changed seriously and the applications functionality suffered.