I am seeing this behavior on a random basis. Its only in Blazor Server. The tooltip on a grid sometimes gets stuck and then the tooltip seems to append fields as you move over different records. I cannot reproduce in a sample as it appears to be intermittent.
Maybe something to do with the implementation? Does it do a signal R round trip on ever hover?
Anyway, my guess is that you are not going to be able to help with this one, but at least it can go on record.