Codesigning fail LC 8.1.5, Xocde 8.3.3

[Ben Rubinstein]

Have proved that Xcode can make a default project, build and install on an 
iPad running 10.3.2.  This is on a fresh MacBook running Sierra.

Used a couple of weeks ago (with LC 8.1.4) for the same purpose (my main 
machine is on El Capitan, hence can't have Xcode 8.3.3, hence can't build for 
10.3.2), successfully. Not used since.

On attempting to update the build, got a load of invalid entitlements stuff. 
Used xcode to reset certificates until it could build again.

Now, under either LC 8.1.4 or 8.1.5, I get a message
	codesigning failed with /bin/sh: line 1: 869 Segmentation fault 11
	...

I'm cranking ahead of a demo tomorrow - any suggestions as to how I go from here?

Many thanks,

Ben