An adjudicator would either agree that the markings were not substantially compliant or not. A subjective decision.
The alternative statutory grounds are that you stopped momentarily at the location in order to move your vehicle off the road via the vehicle access gates, something which should have taken no more than 1-2 minutes.
I've no idea what 'assess the gate' means and I would suggest neither would the adjudicator. Neither do I follow that the vehicle stopped after the 'gate indicated malfunctioning'. 'Stopped momentarily' could be a defence IMO, but as this cannot be proved objectively, then credibility and plausibility come into focus. If the facts, and only you know these, do not fit an alternative approach then I agree that you should focus on the condition of the DKB in the council's evidence and similarly the DKB which are recommended to be repeated regularly in Chapter 3 of The Traffic Signs Manual and which are equally vague, especially when compared to the clarity of the DYL.