Too many off the stacks, a missed approach, weather, disruption/blocked runway, infringer, other priority traffic inbound (PAN etc) and so on. Highly unlikely to be caused by a snatch as they only really happen when the traffic is quite quiet.
The reasons for a longer than usual final or crossing over to the other side are many and varied. Could be any of the above or something else. Not unusual but not ideal either.
In theory you shouldn't go further west than where the north/south base of the TMA steps up from 3,500ft to 4,500ft (about 8nm E of CPT) as that's the western extent of Heathrow's airspace on easterlies, but that does get stretched on occasion!