How to determine meaning of ras-mc-ctl error messages?

ras-mc-ctl --errors is reporting results like:

661 2019-08-20 08:42:29 -0400 error: corrected filtering (some unreported errors in same region) Generic CACHE Level-3 Generic Error, mcg mcgstatus=0, mci Corrected_error Threshold based error status: yellow, mcgcap=0x00000c09, status=0x8c400c400001110b, addr=0x3334c0000080b06, misc=0x00b501c0, tsc=0x3c6571e2bbea4, walltime=0x5d5beab4, cpuid=0x000806e9, bank=0x00000008

and more frequently:

728 2019-08-31 13:35:59 -0400 error: corrected filtering (some unreported errors in same region) Generic CACHE Level-3 Generic Error, mcg mcgstatus=0, mci Corrected_error Threshold based error status: green, Large number of corrected cache errors. System operating, but might leadto uncorrected errors soon, mcgcap=0x00000c09, status=0x8c2000c00001110b, addr=0x2b6b100000374cf, misc=0x0001bdc0, tsc=0x376c4b0d8828, walltime=0x5d6aafff, cpuid=0x000806e9, bank=0x00000008

What do these messages actually mean, and what could/should one do about them?

Additional info:

• This is an Intel NUC 7i7BNH, with 16 Gb memory, 500G SSD, and 4K monitor.
• It runs Ubuntu 18.0, with recent "apt upgrade".
• The BIOS was updated to the recent July version.
• I've made no hardware modifications.

lshw -C memory shows:

*-firmware                
    description: BIOS
    vendor: Intel Corp.
    physical id: 0
    version: BNKBL357.86A.0080.2019.0725.1139
    date: 07/25/2019
    size: 64KiB
    capacity: 8128KiB
    capabilities: pci upgrade shadowing cdboot bootselect socketedrom edd int13floppy1200 int13floppy720 int13floppy2880 int5printscreen int14serial int17printer acpi usb biosbootspecification uefi
*-memory
    description: System Memory
    physical id: 28
    slot: System board or motherboard
    size: 16GiB
    *-bank:0
        description: SODIMM DDR4 Synchronous Unbuffered (Unregistered) 2133 MHz (0.5 ns)
        product: CMSO16GX4M1A2133C15
        vendor: AMI
        physical id: 0
        serial: 00000000
        slot: ChannelA-DIMM0
        size: 16GiB
        width: 64 bits
        clock: 2133MHz (0.5ns)
    *-bank:1
        description: [empty]
        physical id: 1
        slot: ChannelB-DIMM0
*-cache:0
    description: L1 cache
    physical id: 2d
    slot: L1 Cache
    size: 128KiB
    capacity: 128KiB
    capabilities: synchronous internal write-back unified
    configuration: level=1
*-cache:1
    description: L2 cache
    physical id: 2e
    slot: L2 Cache
    size: 512KiB
    capacity: 512KiB
    capabilities: synchronous internal write-back unified
    configuration: level=2
*-cache:2
    description: L3 cache
    physical id: 2f
    slot: L3 Cache
    size: 4MiB
    capacity: 4MiB
    capabilities: synchronous internal write-back unified
    configuration: level=3
*-memory UNCLAIMED
    description: Memory controller
    product: Sunrise Point-LP PMC
    vendor: Intel Corporation
    physical id: 1f.2
    bus info: pci@0000:00:1f.2
    version: 21
    width: 32 bits
    clock: 33MHz (30.3ns)
    capabilities: bus_master
    configuration: latency=0
    resources: memory:dc244000-dc247fff

Test results:

Running memtest86 produced some interesting results:

• After about 5 minutes, it displayed the Intel logo and rebooted.
• The same thing happened again, but I managed to record most of the messages first.
• The third time, it completed a full pass (about 45 minutes), and then crashed again a few minutes into the second pass.
• I'll leave it running, but I doubt it will make it through 4 passes.

The second attempt resulted in:

Test 4: Addr: 33090D380 Expected 08080808 Actual: 18080808 CPU:2
Test 4: Addr: 33090D38C Expected 08080808 Actual: 08080818 CPU:2
Test 4: Addr: 33090D390 Expected 08080808 Actual: [???]
Test 4: Addr: 33090D394 Expected 08080808 Actual: [???]

The third time, which made it through the first pass, showed:

Note that the addresses aren't the same as the previous time (though both had 4 errors).