AirTag position sometimes 2-300 meters wrong - why can it be explained ?

I leave an AirTag on board of a sailing yacht which is moored in a safe port in Italy and I check her position any few days, from Home 400 Km away. How can the position be reported sometimes 2-300 m wrong even on land and few hours later again at the correct spot. It happened 2 times in 5 months.

I am just wondering to understand the technical reason why this can happen. I own 4 Tags, since 4 months, all well charged and perfect working. Same error happens checking with iPhone SE iPad Imac and MacBook pro. Thanks for your opinion.