Grrrr freehub failure

What brand?

Ah yes that might help! Sonder Alpha 29 rear wheel with micro spline freehub.

I had already selected my gear leading up to the dip

Was that 1st gear? Is your chain a bit short and going massively tight under the as the suspension compresses? 

Yes it would have been first gear.

I've kept the chain length exactly the same since it was set up by the shop, it doesn't look too tight but maybe that's something to look in to. 

I'd been on some rough tree roots earlier in the ride, I could hear the chain rattling as I bounced over the roots so I didn't think it was too loose. 

I'm not exactly sure what you mean by "pawl pushed back into the bearing". Do you mean getting stuck inside its pocket and failing to pop back?

If so, it could just be that they've been greased, and the grease is thick enough to stop them returning?

I don't know what make of hub that is - Sonder are probably buying them in from someone (I don't know who) but it's probably a perfectly respectable brand.

I would try returning them to the seller and let them figure it out, but if that's not possible, clean them up, inspect the pawls for damage, check the springs are happy, lubricate - they're pretty simple things at the end of the day.

If none of that works, you could in theory replace the hub (easier than it sounds but a bit time-consuming) or buy a new wheel. Depends on whether you have more time or more money!

Out of the 6 pawls one of them has actually been pushed through the freehub and destroyed the inner bearing/freehub (towards the spindle/thru axle).

Maybe the pawl has failed to bounce back up quick enough (maybe due to the grease?) just as I started to put some effort through the drivetrain? The pawl has got now where to go so the bottom of the pawl/freehub is the weakest point and it gives way?

I can't post a picture unfortunately but if you can imagine a car alloy wheel hitting a pot hole and cracking you sort of on the right track! 

I would be looking to replace it. But with one made from metal rather than cheese.

I've kept the chain length exactly the same since it was set up by the shop,

I wouldn't rule it out just because the shop assembled it/did the PDI! 

Let all the air out of the shock, put it in first gear and compress suspension right down. You should still have a little bit of slack in the derailleur arm. 

If you've 6 pawls and only 1 broken, it should (probably) still work OK. I'd remove the broken bits, dress the damage (or replace the bearing if FUBAR'd), sort the pawl lube viscosity and chain length then see how it is. Our tandem hub has just 3 pawls and on inspection, we'd ground 2 to dust plus one of the 2 freehub bearings - without even noticing it. There's a bit more torque going through a loaded tandem transmission so 1 pawl did pretty well. Caveat, my pawls and hubs are decent Hope's and not Sonder's no doubt Chinese cheesium so that may (or may not) make a difference. 

Alternatively, get Alpkit to fix it under their world beating guarantee...

<edit> Oh, and can you post a pic so we can all see what we're speculating about...

If it's failed 3 times, I'd be finding a new wheel/hub from a more reliable brand. Stuff breaks but thats too often to be more than just 'bad luck'. Need to be able to trust the bits on your bike are reliable...lifes too short for ruined rides with the same damn mechanical

If you go for a Hope hub, they offer a set of "Heavy Duty Pawl Spring" for trails/DH use [ HUB561 ]. You might as well fit them from new.

The Alpkit Alpha free hubs seem to be a bit weak/ problematic- when researching my Broken Road purchase it came up as a weakness in a few search results/reviews.

After doing a bit of research it does sound like the freehubs are made of cheese!

I can't upload images but my previous failures were similar to this:

https://www.reddit.com/r/bikewrench/comments/1jqv385/freehub_failure/

My freehub wasn't anywhere near as chewed up as the example above but after pawl was pushed into the freehub the rest of the damage/metal on the hub was almost identical 

I've had Hope freehubs do the same as that to be fair. 

That's not very typical, I'd like to make that point.

I received an update from Alpkit regarding my wheel last week, I was told a bearing in the wheel failed this time as it had been over tightened (the reverse thread which holds the freehub on, not the thru-axle)

Despite telling them repeatedly that they supplied this wheel last year (as another warranty replacement), I've never disassembed the wheel and it's done a grand total of 80 miles, apparently it doesn't matter and I need to pay £40 for the labour to carry out the repair as it's not covered by their warranty (they're covering the cost of an upgraded bearing). They liaised with head office and I would've been charged more if they had their way.

Being charged £40 isn't the end of the world but being told it's my fault regardless of what I say and not standing by your product when it's done such a small number of miles is more than frustrating. In the end the advice they gave was maybe consider upgrading to a more suitable product in the future (?!). Eerrrrm that's exactly what I did when I ordered the bike! I chose the Alpha wheel set as it was their best wheel set at the time!

I used to be impressed with Alpkit and their products but over time I've noticed a change in their attitude and products. Their good products are expensive in comparison to their competitors and their okay'ish kit can simply be found on AliExpress for much less etc. 

It's a real shame as I could see myself buying another Sonder bike in the future but this whole experience has put me right off.

I'm making the most of a bad situation and considering a wheel upgrade now, I'm tempted by a set of Hunt Enduro Wide wheels (out of the frying pan and in to the fire.....!). At least Hunt are willing to repair/replace and stand by their mistakes! 

I would send their customer service team an email using much of your post above.