`\offsetPosition` fails

[Werner LEMBERG]

I'm using the `\offsetPosition` command
(https://lsr.di.unimi.it/LSR/Item?id=748).  Unfortunately, it fails in
a multi-staff, real-world piece: it has zero effect, and I don't know
why.  What could be the cause for that?  If I had a hint, creating an
MWE would perhaps be more straightforward...

Interestingly, using the 'deprecated' part of this snippet instead I
get warnings like

  cyclic dependency: calculation-in-progress encountered for Slur.positions

but it actually works...


    Werner