Losing G54 position ??

Hi all, and a happy new year .
I've had a rather peculiar problem with coordinate systems on two machines . Both are set to home with index so they should be accurate . But after a restart and rehome, G54 is not exactly where it was left .
Has anybody had this problem ?
Any ideas are welcome .

I think I did yesterday.

I use simple limit switches but I indicated my work piece. I just assumed I didn't notice the dial go an extra revolution but I have no confirmation this happened

I'd expect limit switches to have a bit of discrepancy . But I believe I've had this with index enabled on all axes .

When you say g54 is not the same do you mean the DRO offset is wrong or the physical position is actually wrong?

If it's steppers maybe lost steps or else maybe a loose coupling or mount of the encoder/motor etc. (you didn't mention how much different)

Chris

This is on a well built servo driven machine . And what happens is you set the center of the part today put it in as G54, do a bit of work on that and tomorrow after a restart and a rehome the part is off . Coupling are checked encoders are good . If the machine is not turned off while working the part, all is well .
And it's different every time . It's not an accurate number . It's not off by a complete turn of the screw .

So next I think I would set up a dial and see if the machine homes physically consistent. Either remove the final move part of the homing process or use g53 to remove any user coordinate system offsets.
My guess is that will not be consistent. If it is consistent then that would seem to indicate linuxcnc is not saving/loading the offset consistently (which would be odd)
You also didn't mention the rough error amount . are we talking inches, thousands, tenths?