Sorry, Alan, I’m obviously not making myself clear. If you find that arco refuses to switch to pizz., try adding a “nat.” playing technique before the pizz. playing technique.
And as Paul says there will almost certainly be an issue that we can fix or at the least use to inform the work that we still need to do in this area, so if you can produce a simple and minimal example (e.g. try exporting just one of the string players from your project, then cutting it down to just a few bars that reproduce the problem) and attach it here, we’d be pleased to look into it.