To me it sounds like the internal SSD might've started to fail. If the SSD is connected properly but it doesn't show up at all in Disk Utility, it's most likely due to the SSD failing. If the data is important I would recommend contacting a data recovery facility for options. To repair the device you'll most likely need to replace the SSD. Here's [link|https://www.amazon.com/Odyson-256GB-Replacement-A1465-A1466/dp/B014ZFWPAS/ref=asc_df_B014ZFWPAS?mcid=da7e8473b4113c658212a1bfea7a45d4&hvocijid=8213778333791447737-B014ZFWPAS-&hvexpln=73&tag=hyprod-20&linkCode=df0&hvadid=721245378154&hvpos=&hvnetw=g&hvrand=8213778333791447737&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9033026&hvtargid=pla-2281435178578&psc=1|an option] that I found online. Good luck!