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Tell the LP tec to stick to things he knows and understands.
Yes, obviously CSST does have an inherently high pressure drop when compared to smooth walled steel pipe, but it is virtually impossible to create air pockets due to tumbling. The manufacturer is quite aware of the inherent pressure drop problem and has incorporated it into their design charts/manuals.
Make darned sure that the CSST is properly grounded and jumpered across any brass valves for lightning protection.
Keep looking. You will find the reason for the lock out. It is NOT the CSST.