[Samsung Galaxy Tab A series Questions & Answers] AdvApp:
I have a Galaxy Tab A 8" (SM-T380) which just received a security update (2019-11-30) and now it just constantly reboots -- gets to the logo screen and then just reboots again. Tried using the hardware reset (needle hole) and it didn't even recognize it. Tried holding the Power+VolUp button to get to the recovery screen and that initially displays the blue "Installing system update" screen for a split-second and then it shows a blue Error screen for a another split-second and then goes back to the reboot cycle again.

Looking for some recommendations. The balance of the post describes what I've tried but I found this page which describes applying a custom recovery. Is that my best next option?

I ran Odin3 and, while I couldn't get it into the recovery screen, I was successful getting it to the download screen. I downloaded the FW update (XAR-T380DXU3CSK1-20191125134039) from SamFRew. This page on using Odin said I only needed the AP file, so I selected the AP file and after the MD5 was confirmed clicked start but it failed (see below).

<ID:0/003> Added!!
<OSM> Enter CS for MD5..
<OSM> Check MD5.. Do not unplug the cable..
<OSM> Please wait..
<OSM> Checking MD5 finished Sucessfully..
<OSM> Leave CS..
<ID:0/003> Odin engine v(ID:3.1203)..
<ID:0/003> File analysis..
<ID:0/003> SetupConnection..
<ID:0/003> Initialzation..
<ID:0/003> Get PIT for mapping..
<ID:0/003> Firmware update start..
<ID:0/003> SingleDownload.
<ID:0/003> boot.img.lz4
<ID:0/003> FAIL!
<ID:0/003>
<ID:0/003> Complete(Write) operation failed.
<OSM> All threads completed. (succeed 0 / failed 1)

Further searching led to this page which says you always need to flash all four files. This FW download didn't include the CP (modem) file but I selected the BL, AP, and HOME_CSC and clicked Start again. It says it succeeded (see below) but it is still just back to the reboot cycle.

<ID:0/003> Added!!
<OSM> Enter CS for MD5..
<OSM> Check MD5.. Do not unplug the cable..
<OSM> Please wait..
<OSM> Checking MD5 finished Sucessfully..
<OSM> Leave CS..
<OSM> Enter CS for MD5..
<OSM> Check MD5.. Do not unplug the cable..
<OSM> Please wait..
<OSM> Checking MD5 finished Sucessfully..
<OSM> Leave CS..
<OSM> Enter CS for MD5..
<OSM> Check MD5.. Do not unplug the cable..
<OSM> Please wait..
<OSM> Checking MD5 finished Sucessfully..
<OSM> Leave CS..
<ID:0/003> Odin engine v(ID:3.1203)..
<ID:0/003> File analysis..
<ID:0/003> skip file list for home binary
<ID:0/003> aboot.mbn.lz4
<ID:0/003> sbl1.mbn.lz4
<ID:0/003> rpm.mbn.lz4
<ID:0/003> tz.mbn.lz4
<ID:0/003> devcfg.mbn.lz4
<ID:0/003> cmnlib.mbn.lz4
<ID:0/003> keymaster.mbn.lz4
<ID:0/003> apdp.mbn.lz4
<ID:0/003> msadp.mbn.lz4
<ID:0/003> NON-HLOS.bin.lz4
<ID:0/003> lksecapp.mbn.lz4
<ID:0/003> sec.dat.lz4
<ID:0/003> boot.img.lz4
<ID:0/003> recovery.img.lz4
<ID:0/003> system.img.ext4.lz4
<ID:0/003> persist.img.ext4.lz4
<ID:0/003> userdata.img.ext4.lz4
<ID:0/003> modem.bin.lz4
<ID:0/003> adspso.bin.lz4
<ID:0/003> cache.img.ext4.lz4
<ID:0/003> Home Binary Download
<ID:0/003> SetupConnection..
<ID:0/003> Initialzation..
<ID:0/003> Get PIT for mapping..
<ID:0/003> Firmware update start..
<ID:0/003> SingleDownload.
<ID:0/003> RQT_CLOSE !!
<ID:0/003> RES OK !!
<ID:0/003> Removed!!
<ID:0/003> Remain Port .... 0
<OSM> All threads completed. (succeed 1 / failed 0)