I am just passing along the relative official link, and I hope of you to never need it.
https://siglent.tawk.help/article/instrument-stuck-at-boot-screen-recoveryWhat actually causes a Siglent Instrument Stuck at Boot Screen?
I am sensing poor design of AC/DC power supply, when ACV input this is unstable, and at that time, you store a specific configuration at the DMM.
The combination of the two it might cause firmware corruption.
If you are looking for better answers, call Siglent HQ, if you can.