Ug8lib Arduino and SSD1309 display.

I have a Chinese 128x64 2.4" display with a SSD1309 controller. It works great with the Arduino Uno and U8glib software.
There seems to be a glitch, and I want to find out if it is unstable software, or a display issue. The display jumps vertically, occasionally when the screen is updated. All info is there, but it is 30, 40, 50 pixels offset in the vertical plane.
Any ideas on how to correct this, or soft reset the display to 0,0?