Building upgrade completed instantly instead of waiting for timer

I started upgrading 5 identical spike barriers to Level 2 almost at the same time. All five upgrades showed a construction time of approximately 3 hours. However, one of the barriers completed its Level 2 upgrade instantly, while the other four continued their normal timers. There may be an important detail related to this: This was the only barrier where I had previously used the "Finish Early" option while constructing Level 1. There were approximately 15 seconds remaining on the Level 1 construction timer when I finished it early. Later, when I started the Level 2 upgrades, this same barrier was the only one that skipped the entire ~3 hour construction timer and completed immediately. I received the normal construction completion notification and +100 XP. I restarted the game to check whether this was only a client-side/display issue. After reconnecting, the barrier was still fully upgraded, while the other four barriers were still under construction. So the instant completion appears to have been saved server-side. I haven't tried to reproduce this intentionally yet, but the previous use of "Finish Early" may be related.