1. Your bios is very old. You have 1.8.2 (From 2011) and the newest is 1.13.0 (2018).
2. You have this error in the syslog about the P400.
pci 0000:04:00.0: can't claim BAR 3 [mem 0xbe000000-0xbfffffff 64bit pref]: no compatible bridge window
kernel: pci 0000:04:00.0: BAR 3: no space for [mem size 0x02000000 64bit pref]
kernel: pci 0000:04:00.0: BAR 3: trying firmware assignment [mem 0xbe000000-0xbfffffff 64bit pref]
kernel: pci 0000:04:00.0: BAR 3: [mem 0xbe000000-0xbfffffff 64bit pref] conflicts with System RAM [mem 0x00100000-0xbf698fff]
kernel: pci 0000:04:00.0: BAR 3: failed to assign [mem size 0x02000000 64bit pref]
3. You got the below lines in your syslog, which I don't have. Might be different revisions of the card or that your's a Dell card?
kernel: nvidia: loading out-of-tree module taints kernel.
kernel: nvidia: module license 'NVIDIA' taints kernel.
4. It seems it's a different GPU ID also. Yours is
[drm] [nvidia-drm] [GPU ID 0x00000400] Loading driver
And mine is
[drm] [nvidia-drm] [GPU ID 0x00008200] Loading driver
5. You have the below when the plugin is installed, so there is something going on. Hardware/bios issue is my guess.
kernel: resource sanity check: requesting [mem 0xdd700000-0xde6fffff], which spans more than PCI Bus 0000:04 [mem 0xdc000000-0xddffffff]
kernel: caller _nv030928rm+0x5d/0xd0 [nvidia] mapping multiple BARs
kernel: NVRM: GPU 0000:04:00.0: RmInitAdapter failed! (0x26:0xffff:1227)
kernel: NVRM: GPU 0000:04:00.0: rm_init_adapter failed, device minor number 0
So try to update your bios and see if that works.