I used some Macsim Stump packers last week at the start of my jack n pack adventure and can verify they last at least 5 days. I also used some 6mm villaboard which also hasn’t failed yet. I bought a mix of 2mm and 3mm packers so I can slide them in in small increments while jacking so there is less distance to fall if the jack slips or tips (happened a couple of times). It might also work out cheaper to buy the sized packs instead of a mixed bucket. The my biggest total lift so far is 12mm after pushing out an old asbestos shim.
Check the some earlier posts in the subfloor forum and posts by Optimus in particular.
Also, perhaps upload a photo of the retaining wire so people can see what the issue is.
FWIW I bought a 20 Tonne Kincrome bottle jack from Total Tools for $129 as I wasn’t confident the two 6T jacks I got from Repco a couple of years ago would have enough grunt. The 20 tonner has no trouble at all.
https://www.totaltools.com.au/133490...le-jack-k12159