I have been using Start10 v0.57 since I installed Windows 10 Pro on 16th July and Start10 v0.99 beta for a couple of days now. I really like the improvements and changes from v0.57 to v0.99, especially the inclusion of the proper Windows 10 Start menu icon and the ability to skin the custom Start menus. I have not experienced any major bugs or issues, although my Games menu, like with Start8 previously, still takes 10-15 seconds to populate fully (can Start10 save a database of the games listed here after the initial scan and access that for quicker display?).
Anyway, the only minor oddity that I have noticed is some odd behaviour by the Cortana and Task View icons which are both to the right of the Start menu. Note: that Cortana is NOT displayed as a Search bar but an icon. When I click on Cortana to use it then its icon and the Task View icon can switch places so the Task View icon is to the immediate right of the Start menu icon and Cortana is to the right of Task View!!! Sometimes they remain that way until I again click on Cortana and other times I can see the icons randomly swapping places as I watch. By default these two icons cannot be moved; the Cortana icon is to the right of the Start menu icon and the Task View icon is to the right of Cortana.
Here is a screenshot clearly showing the issue with the Task View icon appearing to the LEFT of Cortana:

I did not notice this behaviour with Start v0.57 unless I missed it and it was occurring. Of course, it may just be a Windows 10 bug, of which I have found plenty, but I thought I would report it here nevertheless.