Anchors Not Working After 3 Anchors

Hi,
I am trying to put anchors in to make navigating through long pieces of text easier. The trouble is, the first 3 work but then after this they stop working. The codes I am using (got from this site) are:

Bact to Top

Can anybody tell me what I’m doing wrong?

I have seen codes which insert the title of the piece but I don’t want to do that as I already have my titles nested within spoilers.

I see there are plugins for anchors; can anybody vouch for any of these?

Yours frustrated,

Angela3000