Oddly enough I find the security staff at Gatwick strangely far friendlier than any other airport I travel through. Don’t know why but they generally are. Even when last year (I had packed my hand bagage some days before travelling) they found a small bottle of water in my bag - took me aside and searched my bag, made a joke about it - asked me if I wanted a drink before they took it off me. Yes I was a numpty but handled brilliantly.
However these ‘inconsistencies are what you get when you have different companies involved in the chain of getting you onto an aircraft (Check-in staff / security staff / flight attendants). Neither in the chain want to be responsible for ‘misinterpreting’ the overall rules so all apply them to the nth degree using inconsistent logic. You probably wouldn’t get this if they all worked for the same company as a culture of trust would develop and it would be easier to spot who wasn’t doing their job properly and it would be easier to transfer responsibilities up and down the chain and folk would work together.
As an aside, when flying from a certain large west of England aiprot recently, my colleague commented (genuinely) to the security staff on how speedy they were and how it was his best experience for a long time. Their reaction - ‘thank you sir, how kind’ nope ! threatened to stop him flying for being sarcastic !! You can’t win with them.