Your method and application appears sound but it did not work. Oh, Well...

Sure sounds like a problem with dissimilar materials in the components. Or a common failing of newer vulcanizing cement that does not contain Toluene. Toluene is a vital component of having a good bond in vulcanization. Of course like many things it has been found to be carcinogenic and therefore is on the Stigma List.

In my flat fix kit I keep a small tube of unopened Vulcanizing Cement and an unopened Tube of Super-Glue just in case the Cement has dried out.

Further note that over the years, although some people have, I have never had a successful seam rip repair on butyl tubes.