Very Strange GPS Problem


i´m flying with arducopter since begin of this year.
I like it and most problems are solving by myself.
Now i have a very strange GPS problem.

I bought an used apm 2.5, thinking it´s a clone.
Software is 3.1.5 and Mission Planner 1.3.9

I have many Error-GPS 0+2.
First GPS was a V3 from RCTimer. It was very good.
Suddenly there was many errors.
So i changed to a cheapest GPS from beginning…same effect.
The strange thing is, Loiter is very good…1 to 2m difference at windy day.

I hope someone can help me.
[attachment=0]gps glitch.jpg[/attachment]

No one an idea?