Somewhat common, but it can be a problem. The issue is the retaining nut on the inside of the hull is loose, allowing the plug assembly to spin. If it's on the left side where the iBR is, it's nearly impossible to get to.
Get someone to hold the outer ring of the plug assembly while you try to remove the plug. If it won't budge, just leave it and don't use that plug for draining.
My entire plug assembly came out years ago and I couldn't get it attached as securely as I needed, so I did the best I could and then applied RTV silicone clear sealant around the plug assembly to keep water from leaking in.