Flicker/dim when subtitles appear

Hi all, been around for some time, unable to find any topic related, here or on the whole internet. Maybe it is related to my lack of English, so apologies if this is not the place to ask or if it has been posted already. On top of that, I do not know for sure if it is a issue related to the OSMC itself, but my guess is I can get help here. Thanks in advance for support.

I have the following, running smoothly:

-Raspberry Pi 3 Model B with OSMC connected with a “standard” HDMI cable to
-Denon AVR-X1100W, connected with a HDMI 2.1 to
-Sony 49XD8305

When I am playing video with subtitles, every time that a subtitle appears, the image dims (or flickers, or goes dark) a bit, very briefly. If a second subtitle comes immediately after the first one with no pause in between, I don’t get the flicker (e.g. first part of a phrase, followed by the second part); I only get the dim when a new subtitle appears on screen. Difficult to explain, again, sorry for my English, I hope it is understandable.

I think it is related to OSMC due to not having this problem when watching subtitles in any other platform, like Netflix, cable TV or similar. I have not found any similar problem in the net related to the TV (which is relatively new). Only happens with OSMC.

Do you know if I can get to modify some settings in OSMC to try to eliminate this dimming/flickering? Do you have any idea of any test or information I can get to try to isolate the problem to some video format or anything to try something?

Thank you very much for reading and supporting.

To get a better understanding of the problem you are experiencing we need more information from you. The best way to get this information is for you to upload logs that demonstrate your problem. You can learn more about how to submit a useful support request here.

It would also be good if we could find out more about the file you are having issues playing. Please see the mediainfo section in How to submit a useful support request - General - OSMC

Thanks for your understanding. We hope that we can help you get up and running again shortly.

A sample file that is known to show the problem would be useful.
A recording of the flicker/dim effect (e.g. from a camera phone) would help understanding exactly what the effect looks like.