We have installed SL1000's, SL2100's, SV8100's and SV9100s, never had one crash to the point of replacing the motherboard (SL1100) or the CPU blades on the others and have to upload the saved data base. In short they all have been very reliable.
OK I'll knock on wood for lock.
NEC actually had a bad batch of SD cards for the SV9100 in early 2018. I had one location fail twice in a six week period. Something gets corrupted on the SD card and it will cause the CPU to fail. Had to replace the CPU and SD both times. Phones will have the date and time on them but will not process calls and then if you reboot it, it will not restart. Can't boot to a USB to force an upgrade, nothing. NTAC knew about and would ship out replacements right away.