PLC5 Analog Values Overwritten on IFE card?

In our PLC5 processor we have the last analog value being overwritten on a couple of cards.
The values from the next card down are being sequentially written over the last analog value of the previous card. (see pic)
I looked in Block transfer programming but can't see any errors.

Since this is a PLC-5 system and has been presumably running properly for years, what has recently been changed?

Yes, it has been running for years, and for example N11:11 (SAPP Tank temperature in pic) In the N11 data table stays constant at 1300.
But when you look at the data column in the IFE information page the N11:11 value flips to 287 (from N11:16)
then 1573 (from N11:17)
then 1573 (from N11:18)
then 586 (from N11:19)

The value is changing in the data column (white column) but not the data table value....
Could this be caused by a BTW or BTW setup wrong?

what I would do is to search for the first register that is changing which isn't supposed to - do a global search all.

that will tell you every rung where this value is being written into.
remember, the last rung that references the register is the owner !

repeat for the other registers.
james

The only place N11:11 (for example) is being written to is in the BTW of the Analog input card.
But it's not the value of N11:11 that is changing, it's just in the white data box of the Analog module information page.
The values from the other analog card keep cycling in through the data box.