When mining obsidian, just as I'm about to dig it out, it will suddenly auto-pathfind for a moment. Is there any solution to this problem?

Are you using Baritone to mine or are you mining yourself (or using something else).
Do you have other mods installed?

I already know the issue. It's a problem with the server I'm playing on. In my single-player world, everything works normally, but it doesn't work properly on the server. I tested the time it takes to mine obsidian in both environments - 3 seconds in single-player and 9 seconds on the server. I suspect that's probably the reason causing the aforementioned issues.