Well this prompted me to check my expert logs. I won't list them all out here, but the common issue is to do with the "stdlib GBPUSDSB,M15: loaded successfully" line, which is mentioned in your log as well; only difference is that mine includes 'order timeout'. It is always associated with a 'no connection' comment in the MT4 log (same time stamp).
For trades prior to 3rd May there are no problems opening trades, and no sign of the above mentioned comments in the logs.
The SLM demo account logs show no problems with the connection and no stdlib comments, and it took the same trades!
So there are apparently no network issues here, it is pointing squarely at the SLM live server.
I continue to be somewhat confused by SLM's view that there must be a problem with the EA and not themselves, as I have had an SLM demo account running now for about 3 months, which not only never misses a signal, it is comparable with my demo ThinkForex account and mostly completes the trade several seconds before 6.15 (today the journal says 6.14.45) and I'm using the latest MT4 build on both accounts - this begs the question - if it works perfectly well as a demo - why do they have a problem when people convert to a live account?? - (a question from a mere simpleton, not a techie!). At present I doubt if I'll be opening a live account anytime soon with SLM, more likely to be with ThinkForex, but for the time being I'll continue to trade with IG manually