PIP renewal success?

So I got the decision on my PIP renewal in the post today.

Some information: form arrived in December, returned in January. Assessment in May, report arrived with DWP 3 weeks later.

Previously I was in receipt of the Mobility Component at the Higher Rate. Now I'm getting Mobility and Daily Living at Standard Rate.

The new rates start as of last week, and I got a backpayment of Daily Living back to December. However, there's been no deduction for the drop in Mobility Component, which my partner is really worried about.

There are also a couple of errors on the award letter. It says that I was previously in receipt of Daily Living and that Mobility is new.

I'm not normally one to complain when something appears to have gone in my favour, but we were wondering whether to request a Mandatory Reconsideration as I dropped from 10 points to zero on Planning And Following A Journey but my partner, being a worrywort, is adamant it could jeopardise everything and I could end up with 0 points across the board and they'd demand the entire backpay amount back as a lump sum.

We're still waiting for the Medical Report, which has been requested, so we'll give that a poring over when it arrives.

Is it usual for them to not request any money back if an award drops, but being due backpay on another part of it?

The backpay is the entire amount as the Daily Living but with no deduction for the drop in Mobility Component.

It says the award starts 9th August 2019, but the backpay is dated back to 7th December 2018, but there's no explanation as to why this is. Is that standard practice or is it at the discretion of the DM?

December was when I got the re-assessment forms as it was the earliest they could reassess me.

My partner rang DWP since my last post and was told the arrears were Daily Living from December, and the reason it read strangely to us is because it was likely a "Split Rate Decision".