Where is a solid NAS supporting SSD-Cache?

Hi there. I own 8 old ReadyNAS. All of them run perfectly and are flawless even after 10 years of use! 4 years ago I bought an Asustor AS5104t and upgrade it with SSD-Cache (2xWD RED 4TB + 2xWD blue 2,5" SSD 250GB). After 3 years the display stopped working. A year later I started the automatic operating system update. In result the update stopped after 30% of software download and connection failed. Since that time system can not be used any more and ends into hardware crash. Unbelievable! A software update ruins the hardware! By the way Japanese forums are full of same experiences! After that bad experience I searched for a solid system like ReadyNas. Unfortunately ReadyNas do not support form factor M.2 2280 for SSD-cache. So I bought Synology DS918+. Machine runs well but I do not trust the hardware. VERY poor case made by plastic. Do you have any idea which NAS will fit my need? Solid hardware and fast into storage. Best regards Winfried