Prohibited symbol on boot

I purchased a used Late 2012 i7 with 16 GB of RAM & a 2.25 TB Fusion Drive that was running High Sierra,

The computer seem to be working fine, until just before Christmas it booted once and I got the prohibited symbol. I had not yet moved things over to it so I did not loose much. I rebooted into recovery and reinstalled the OS.

It worked fine for a few days then it happened again. I ran disk utility in recovery mode then disk first aide without much progress. I reinstalled the OS through Disk Utility and 6 hours later I was running again but hesitant to use this machine as a main hub for photos and my iTunes library now that I have had 2 crashes in a few days.

I have searched the web with little to show for it.

I ran Ertchecker and came up with the some results however my post has been deleted 3 times already and i think that is why.

EtreCheck Report

Is the drive failing or is there something else? RAM? The SATA Cable to the drive?

I also saw on this: Upgrading from HDD to SDD, but get prohibitory symbol when booting up?. Is this possible?

I thought It might be my 2TB mechanical drive was starting to fail but searches on the internet came up with nothing.

I now see looking back through one of my RAM chips was not seated correctly or is starting to fail. I know when I got the computer when I ran system profile that the I had 16 GB of RAM. If one ram chip was not seated would it boot at all?