Under the View menu, make sure that all of the Snap commands are turned off (no check mark).

In the Transform panel, make sure that Snap to Pixel Grid if turned off. (That command may not be in Transform panel, depending on your version of Illustrator.)
If you're using Illustrator 2017, select the text object and turn off this icon in the Control panel.

If the object still jumps all over, try zooming in more closely.
If none of this works, the file may be corrupt -- if that is the case, let me know and I'll make additional suggestions.