Large sidebar incorrectly laid out on page load

[calliecameron]

When there are a lot of things in the sidebar and the sidebar is taller than the window, the sidebar is laid out incorrectly when the page loads: some sections are off the bottom of the page and inaccessible, and scroll buttons are missing. After resizing the window, the layout is correct: all sections are visible and have scroll buttons. The layout should also be correct when the page loads. I've seen this happening on firefox, chrome and chrome for android.

On page load - there's supposed to be a 'trains' section (added by https://github.com/Zhincore/dynmap-trains), but it's completely off the bottom of the page because the dimensions section is taking up so much space:

After resizing - even back to the same initial size - with the dimensions and trains both visible and with scroll buttons:

• Dynmap Version: 3.7-beta-4
• Server Version: fabric 1.19.2
• Pastebin of Configuration.txt: https://pastebin.com/5SETL3z2
• Steps to Replicate: I'm specifically seeing this happen with extra dimensions from Ad Astra and trains from https://github.com/Zhincore/dynmap-trains, but I'd expect it happens with any long sidebar with many sections.

[y] I have looked at all other issues and this is not a duplicate
[y] I have been able to replicate this