Yup, nothing for those dates. Whenever there is a holiday, or in this case no prices posted, the TSP Talk page just duplicates the prior business day's prices.
https://www.tsptalk.com/tracker/tsp_fund_price.php
Correct, but the market was open Friday 5/27 and Tuesday 5/31. The prices posted are from Thursday 5/26 for both 5/27 and 5/31. So it appears that TSP is considering 5/27 and 5/31 as a holiday period.