Yes I agree and lots of us have had the same annoying occurrence.

Weird stuff happens that unless we worked in IT at IG we prob will never know why?

Is slippage a factor in your example … you will never know?

I’ve been manual trading a lot today and about 6 times when I clicked to Exit (both Long and Short) I got the message … ‘That Price is no longer available‘. As my Exit instruction was at Market Price then I can’t help thinking there are algorithms at work behind the scenes and in my case of not being able to Exit was due to a flash (milliseconds) widening of the spread or the minimum distance parameter or some other IG machination?? 🙁

In short … there isn’t always an answer (not visible to us anyway) and you may drive yourself  bonkers trying to find an answer??

I just though of one thing though we had a while back, I worked on with one guy … the calculation of Indicators were not exactly the same on Backtest and AutoTrade / Forward Test.

Have you Graphed all your conditions? Ah, but of course you cannot GRAPH on Forward Test anyway so that trail dies there??  🙁