Your work is probably all exiting through the same IP, you competing with others on the same IP is causing the rate limit.
The very same thing happen on my residential connection, I can do one search query, then I'm rate limited for 15+ minutes, same if I access any list of commits.
May explain the ipv6 resistance. Hard to do effective per-ip rate-limiting with v6.
I've considered this, but the company is small enough that the number of people who would be on GitHub at any moment (instead of our internal git forge) can be counted on one hand, and when I'm the first one there in the morning it still rate limits me.