Thank you for playing, and I'm glad you're enjoying the game! The run does save to an extent when closing the game, although the exact state of the battle you're in is not saved so it's best to stop playing a run right at the start of a battle.
In terms of the freezing, the list of words is pretty extensive, especially for longer words, and it does take some time to search through them all. I've done what I can to lower the time this takes but due to the limits of the device the search does still take time. Luckily it's never more than a few seconds (you should have seen how bad it was when I first started working on the project!) so hopefully it's bearable.
I appreciate your feedback and hope you continue to enjoy your time with Rendsword!