GM 0.280 alternating bad~84% good~100% CRT tv

[nix999]

Hi,

I have an issue I cannot solve. I am on a custom build Arch with KMSDRM attached to PAL scart television.
I am currently running a custom kernel 6.17.7-arch1-15khz-1.
The TV set can sync to PAL and NTSC ( at least, I have a stable image at 60Hz).
The shell is PAL 768x576i@50Hz when the system boots so that I have somewhat decent visibility when accessing it directly though I mostly use ssh.
I have all graphics and sound working but ...
When using GM 0280 I get alternating bad and good runs.
I defined these two in mame.ini ( the latter two make no difference )
crt_range0                15625.00-15625.00, 50.00-50.00, 1.500, 4.700, 5.800, 0.064, 0.160, 1.056, 0, 0, 192, 288, 448, 576
crt_range1                15734.26-15734.26, 59.94-59.94, 1.500, 4.700, 4.700, 0.191, 0.191, 0.953, 0, 0, 192, 240, 448, 480
#crt_range0                15600-15700, 49.5-50.5, 1.5, 4.7, 5.8, 0.064, 0.160, 1.056, 0, 0, 192, 288, 448, 576 # PAL-like 'wider' range
#crt_range1                15700-15800, 59.0-60.5, 1.5, 4.7, 4.7, 0.191, 0.191, 0.953, 0, 0, 192, 240, 448, 480 # NTSC-like 'wider' range

When launching for example sf2 I have this:

(The game is being identified as
Switchres: get_mode(0) 384 224 59.637405 1.333333
Switchres: Calculating best video mode for 384x224@59.637405 orientation: normal)

- system boot and then

BAD:

Switchres: Modeline "384x224_59 15.704280KHz 59.940000Hz" 7.271081 384 395 429 463 224 235 238 262   -hsync -vsync
DRM/KMS: <1> (add_mode) [DEBUG] Adding a mode to the kernel: 384x224 SR-1_384x224@59.94
DRM/KMS: <1> (add_mode) Mode added
Switchres: added DRMKMS timing "384x224_59 15.704280KHz 59.940000Hz" 7.271081 384 395 429 463 224 235 238 262   -hsync -vsync

Average speed: 83.85% (26 seconds)
Enter sdlwindow_exit
Switchres: success deleting mode DRMKMS timing "384x224_59 15.704280KHz 59.940000Hz" 7.271081 384 395 429 463 224 235 238 262   -hsync -vsync

GOOD:

Switchres: Modeline "384x224_59 15.704280KHz 59.940000Hz" 7.271081 384 395 429 463 224 235 238 262   -hsync -vsync
DRM/KMS: <1> (add_mode) [DEBUG] Adding a mode to the kernel: 384x224 SR-1_384x224@59.94
DRM/KMS: <1> (add_mode) Mode added
Switchres: added DRMKMS timing "384x224_59 15.704280KHz 59.940000Hz" 7.271081 384 395 429 463 224 235 238 262   -hsync -vsync

Average speed: 100.70% (17 seconds)
Enter sdlwindow_exit
Switchres: success deleting mode DRMKMS timing "384x224_59 15.704280KHz 59.940000Hz" 7.271081 384 395 429 463 224 235 238 262   -hsync -vsync

BAD, GOOD, BAD, GOOD ....

There is no difference but the Average speed.

I already tried to add a one second sleep after the mode has been added in function 'bool drmkms_timing::add_mode(modeline *mode)' in 'custom_video_drmkms.cpp' to no avail...
It kicks in but no change.

I also tried
   parsing switchres.ini
   Invalid option mode_delay   
Because I read that somewhere but that does not or no longer exist ... it is not easy to find spot on information.

I do not really understand what is happening but I think it has to be some timing issue but it is 100% consistent in behavior.
How can I solve this please?

Thanks for any help.

GM log attached.

[nix999]

I experimented some more and started afresh with a new mame.ini created with -cc.
So I now have a pristine config. As fresh as it can be.
I made sure it finds the roms.
Next to that the only option I modify is: monitor
I tried pal, ntsc, generic_15 and arcade_15 with the wboy rom.
Whichever one I choose I always have the BAD, GOOD, BAD, GOOD ... speed-wise.
There is of course a difference between the four. ntsc and arcade_15 performed best while pal was jerky even thought the emulation speed was 100% in GOOD runs.
Where does that alternating BAD GOOD come from?
Anyone?