duh – found the issue with this –
we had an XLT file with an incomplete condition line in an IF.
{ COND { 0(0).MSH.#9.[1] eq =A02 && 1(0).1(0).PV1.#10 eq } }
should have had a value tot he right of the a second eq.
hcixlttest on just the xlt file didn’t indicate any syntax error/failure to load, although once a message occurred (or was run through the tester) we immedaitely got the same assertion failure.