My mum had multiple financial investments (£5000 here and there) and I went in person where I could, and even then some needed 3 bits of ID from me instead of the standard 2.
However some of the postal ones wouldn't accept the certified LPA as they needed extra lines written on, eg hand written instead of the solicitor's stamp. When I phoned and pointed out what was a validly legal copy, they said well these are our rules. So I went to the solicitor's with my certified copies (I have 5 as so many to deal with) and she went through each letter with me, and wrote what each one needed - each one was different, and they needed different things on my passport as well.
Her charge was minimal £10 for the original 5 and I think only £5 for the amendments - I did actually try and pay her more as I thought she wasn't charging enough.
I actually haven't finished my mum's stuff as it was such a nightmare.
It is very frustrating that due to poor understanding of LPA's financial organisations have put extra hoops in.
Ultimately an organisation is entitled to create their own rules as to what they require and set the bar higher. Maybe we need a Martin Lewis type crusade against it.