I’m going to render the same list, increasing the start attribute by a place value for each subsequent one:
1. Betsy
1. Tacy
1. Tib
1. Naifi
- Betsy
- Tacy
- Tib
- Naifi
- Betsy
- Tacy
- Tib
- Naifi
- Betsy
- Tacy
- Tib
- Naifi
- Betsy
- Tacy
- Tib
- Naifi
- Betsy
- Tacy
- Tib
- Naifi
- Betsy
- Tacy
- Tib
- Naifi
I’m able to reproduce. It is a CSS issue, in that the default space around ordered lists (<ol>) is normally set to accommodate lower numbers.
I noticed the same lists render differently per theme, so I created a theme component that just added:
ol {
margin-left: 3em;
}
On the other hand, this also applies to all lists, and when the item is not a large 5+ digit number, the ordered lists look like they have too much space…
My suggestion: apply a component that matches your use of ordered lists on your site; I think it is rare to excerpt the middle of a very long list of items, and I can’t imagine someone posting lists with 10,000 items without running into character limits. 
I thought maybe there was a way to style it so a given list would always fit, but the numbering in ordered lists is applied as psuedo-element (::marker), and I’m not sure how to do CSS math on those… 