Map bug

Ever since 20w17a, creating a map in older worlds results in scattered lines over the top showing the layers underground.

What I expected to happen was...:
prior to 20w17a, the maps in a pre-existing world worked perfectly fine

What actually happened was...:
when 20w17a came out I created a map and it gave me the glitchy map texture in the attached image below.

Steps to Reproduce:
1. go into a pre-existing from 1.15 world using a current snapshot

2. create a map