At my store we had a much the same situation going on with SPU RTS, it was terribly red, and became a focus. It was a challenge because there are two work centers that could be causing the errors. Guest service team blamed the FF team, the FF team blamed GS and AP blamed both, so much fighting over one metric. So I can relate. This is what we did to improve the score.
Our store is much like one SFSfun mentioned. We have a clipboard up front (there is a SPU log template available on workbench) where the GS team takes the pick sticker from each order and place on the log sheet along with their initials, date and time of pick up.
We also have another clipboard for the FF team if they come across a RTS that is not present, (this helps provide a check and balance system). I had to make it on excel there is a column with date, dpci, and quantity.
This provides a clear timeline for either AP or whomever at your store might investigate.
It helped at my store, because now there was accountability (which there always should have been). We found out some GS team wasn't trained properly at handling SPU orders on MyGo and there was a FF team member who wasn't actually checking just "clearing" the list in the morning.
Some tips:
If your IPad is having issues, you can access MyGo on a mydevice to checkout guests.
Also there is template on workbench if MyGo goes down for GS to fill out.
It took a few weeks to find the problems but our RTS has been green.🙂