have you tried googling "TPLink - VX230v enable ipv6"?
I hadn't actually but I gave it a go and it helped me find a setting I hadn't noticed - The EWAN settings didn't have IPv6 enabled. So now I have IPv6 working (but dingbats to IDNet for not configuring the router correctly).
Anyway, thanks for your suggestion!
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Andrue Cope
Brackley, UK