I had a problem with my Savi's light saber that I purchased back in 2019 but the problem is not what your son is experiencing. My blade lit up but it was only red, no matter what kyber crystal was in the hilt (yellow, blue, purple, green). I tried to speak to Disney Customer Service BUT they were completely clueless about this item. They wanted pictures etc but couldn't view anything I sent them & this went back & forth for WEEKS. I just gave up working with them because they could not help me. I went back to WDW in March 2021 & brought my malfunctioning light saber with me & at the Savi's check in desk, I explained my problem. The CM took my saber in the back & brought it back & told me she had to change the hilt core & even the blade. I also mentioned that my carrying case had a hole in it & she gave me a brand new one. Everything was replaced at no charge which amazed me. I'm sorry, I didn't ask if there was a number to call to get assistance for people who are not in Florida any longer.
Initially, my blade was jammed into the hilt incorrectly so we had to force it out. Have you tried to take out the blade & reseat it? Push in & twist or twist & pull out?