When you look at the Carrera Zelos the dropouts actually look very over-built but there are always going to be the odd poorly made frame. Halfords despite having a huge chunk of the UK market have had very few recalls. I seem to remember the Carrera Banshee had a recall which was a dual suspension bike and the pivot had an issue or something, can't be bothered to google it. Compare this to major competitors like
Decathlon who have had a huge number of recalls. However recalls only kick in when a small but significant number of bikes have issues.
There are lots of ways a bike can have issues at the rear. The Zelos is an entry level road bike with I believe a quick release but a freewheel which means the axle is unsupported and if the axle snaps i.e. hitting a pot hole or dropping off pavements etc then the wheel may lock putting the frame under a huge amount of stress at the rear. Many entry level road bikes are configured like this but I would always suggest paying a little bit more for the Virtuoso bike which offers so much more in specification for only a little more in price. The Zelos looks pretty over-built with regard the rear dropouts looking at this image.
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If the frame is damaged and they replace it then I would suggest an upgrade to a freehub rear wheel with a 7 speed cassette like 11-34T. This will offer much better high gearing, improved safety and strength, cleaner shifting. The Zelos is a nice bike and this situation is very rare I would say but the sweetspot for value I feel is the Virtuoso model which offers a Claris level groupset (probably a FSA crankset).