Has anyone considered the weather to be a possible factor yet. The weather may appear to be benign but what is actually happening to an airmass is often unseen. Summer weather often produces unseen thermals, rising columns of warmed air with associated areas of sinking air. This often produces sea-breeze fronts near the coast and sometimes moving well inland. On the coastal side of a sea-breeze front there can be very large areas of sinking air, such areas going up to several thousand feet where the entire air mass may be going downwards at several hundred feet a minute. Suppose the airmass is descending at 300 fpm (not unusual) and an aircraft within it can perform a loop in 20 seconds and finishing at 100' agl it will have lost an extra 100' so end up at ground zero. Do display pilots factor this possibility into their displays.
I was not there and have not seen the weather reports, but if there were lots of fluffy cumulus clouds visible inland but none over the airfield and out to sea then there is a possibility that there was a large mass of descending air in the area, particularly if an unseen front had only recently passed through. The passage of such an invisible front would be normally be indicated by a change of wind direction along with the line of cumulus clouds moving further inland. Of course, in many instances there will be no cumulus but there will still be thermals and still be a hidden front with its associated large area of descending air.
Another possibility, if the wind is from a northerly direction, is wave effect caused by the hills to the north. Again, there may be visual clues from wave clouds but not always. Again, these can produce very large areas of both rising and descenting air in the order of hundreds of feet per minute.