Hi Tim,
I must admit that the 'lap analysis' tool is not well documented or obvious in its use. It determines the start of the lap by the first point in the first track in the file. You may need to trim down the first part of it in order to get it to behave better.
As for merging the files, which method did you use to merge? Did you use the 'merge tool' to click on the tracks in succession? Or just the 'merge files and save as...' option? If the latter, it may be that one or more of the laps is stored across two files, so that lap really needs to be merged as a single track, across the files. It can be tricky with overlapping data like that.
Apologies for missing this reply -- for some reason I didn't get an notification as I usually do on a new post.
Cheers and congrats on 15 laps, dang!