WIring is fine, looks like the correct stuff is there. Builders often use bell-wire which is bad for broadband, but that isn't.
It might be worth checking both extensions to make sure the White/Blue goes to T5 in the same way as on the master. If there is a swap-over that is not good.
From what I can see of the master socket I don't think the ring wire would have mattered, as I think it is filtered anyway. But no contact cannot fail, a filter can.
Which ISP and package is it? "Boost" sounds like Plusnet or TalkTalk, but it may be some other one. Other factors can be affected by the ISP, such as the noise margin settings, mentioned by XRaySpeX, so we can't really advise on that without knowing.
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