EDIT (3 July): We have now rolled out a new update 30.0.1 for all players, which should fix this issue. Please update your game!
30th of June, 07:00 AM UTC: There is a known issue with Troops during gameplay Battles in the Sand Empire Summer Event. We are currently investigating the issue here. We will update this announcement with any new information.
You may also follow the thread on our Community Forum regarding this issue, and to see any updates posted there: Sand Empire Bug
We hope to fix this issue as soon as possible. Our apologies for any inconvenience caused by this issue!