Hello! I experiencing this problem from starting using Zoiper (two weeks ago) to nowadays.
Today i updated Zoiper to newest version, but problem exists.
If i use Force background mode, all my audio (and Zoiper ringing) changes to ear speaker and sounds very silent. I missing calls and can't normally use iPhone without audio.
Any suggestions to fix it? I waited for update, but it didn't fixed.
My iOS version is 9.3.2