From PolitiFact:

• Social media posts claimed that primary voters were not allowed to cast ballots at certain voting sites in Texas on March 1. Posts alternately claimed it was Democrats or Republicans that were being excluded.
• Many counties experienced a shortage of election workers. So the voting problems were likely real, but they did not appear to be not widespread.
• Texas primary procedures are also to blame. County parties are responsible for hiring election workers, and in some places one side or the other did not adequately staff their voting site.