This bug returned from past
After you chose the speed % if you click to go next (in italian ogame the label is "AVANTI") but before the command is executed (next fleet page loaded) you leave the mouse on a different speed %, a wrong speed% is chose (the speed you leave the pointer on).

This happen in antigameorigin v5.6.1 for firefox (addon)

screenshot attached

It's an OGame problem, should be fixed with OGame 5.6.0 - do you still have this problem or it's from the last days ?

No, bug disappeared!