I tried again today (6 days later), and download was successful. Perhaps that was just some network or ISP problem.
Now, however, I'm getting an error when I try to run.
BeaverSim [version: Unity 2017.2.5f1 (588dc79c95ed)]
UnityPlayer.dll caused an Access Violation (0xc0000005)
in module UnityPlayer.dll at 0033:daf13dcb.
Error occurred at 2021-06-11_155354.
C:\Users\<user>\Downloads\SotE 0.15\indev.exe, run by <user>.
26% memory in use.
16271 MB physical memory [11986 MB free].
18703 MB paging file [13911 MB free].
134217728 MB user address space [133885694 MB free].
Read from location 00000008 caused an access violation
...