MikroTik rb750gr3 checksum issues

I'm having a strange issue with an rb750gr3. I was able to boot and install a snapshot to the router without issue. After several days, it went all sideways. The first symptom was that Netflix quit and the throughput to fast.com went to ~4Mb. I tried to upgrade to a later snapshot but when attempting to upload the file through Luci, the SSH session with the tunnel drops. I tried without the tunnel, connecting directly to port 80 with the browser, and the checksum doesn't match the file I uploaded. I tried SCP and the session disconnects when the transfer starts. I also tried wget but the file arrives corrupt there as well. I'd blame it on a hardware failure but it PXE boots fine, pulling the 3MB+ file seemingly without issue. Anyone have some wisdom to offer?

When this happens to me, The first thing I check the disk/RAM space available (typically some things can take a lot of space quickly - logs, opkg updates...). Also make sure that you consider what is already in RAM if you scp your file to /tmp (tmpfs is in RAM which means all your /tmp, /var, /dev is already using that RAM).
If you are going to flash from scratch anyway, you could always reset your device (clean things up) and try the flashing again with minimal space in use.

I performed a reset using umount /overlay && jffs2reset && reboot now . df -h reports 123.3M free on /tmp. The sysupgrade file is corrupted if I use wget and winscp terminates connection upon starting the transfer. I pxe booted the latest snapshot with the same issue.