Have you tried same with analog side BW reject.
So far this issue has *not* reproduced with the 20MHz bandwidth limiter enabled on the probe. Looks to me like whatever's causing this, it's very high frequency noise that somehow doesn't appear in the capture.
I'll try some of the other things next.
This is very strange if it do not appear in capture or captured raw ADC data. It must be there, infinitely. Without it, it do not trig. But all is possible. Also some bug in FW what cause this reason is hiding.
Do you have FULL .CSV or Binary data. Screen shot png and paired with this full saved sample data. Example 3 set of these pairs so that these pairs are somehow marked so that can not mix and with perfectly explained trigger setting and scope other settings (norm/Auto, possible trigger coupling filters and, trigger setup exactly and so on. (display dots/interpolatin line or sinc do not affect any thing, they are post processed.)
Because if there is really no raw ADC data what explain wrong/failed trig, it need solve what make it. These can bit look and forward to Siglent for further analysis. It is not lottery machine and it do not have its own mind what some times do irrationally something like human..
Are we absolutely sure the trigger voltages are converted to adc values, and not let's say analog comparators? The strange thing is that when using scpi those voltages are attributes of each channel. In a complete digital situation, it would be more logical for them to be attributes of the trigger.
It could explain the behavior if they where analog...
How many times it need say: Siglent trigger engine is totally and fully in digital side.
If you do not believe, please take one SDS on table and parts... and try find analog trigger side pathway from it, starting from BNC and ending to ADC input. If you today find low price segment new DPO and it use analog trigger system just throw it out from window as fast as it arrive to your hand. It belongs to museum.
Siglent is not Keysight IV machine what still have analog side pathway trigger engine lika in old times mostly all DSO.
Also Siglent OLD DL/CNL/CNL/CFL series have analog side pathway analog comparator trigger system
All X models have full true digital side trigger system.
Only exception is ExtTrig input in some X/X-? models. It is analog trigger where trigger level to compatator ís done using DAC.'
If you do not know what is true digital side trigger system you can find example nice Rohde&Schwarz explanation about it.
With these kind of Trigger things what are example in Siglent and many other modern scopes is quite difficult to do with analog trigger using simple circuits.
Of course now this case rise one question. These trigger things are complex and time critical things deep inside system. Always is possible that we hit some unexpected error. These are so comples no one can never test all combinations in product development. If some say it can he do not know what he is talking. So, this possible need keep in mind until further data and tests.
We have now ONE thing what is clear it affect. BW limit. Other things like more wide slope rising time limits did not affect. Now I am not sure if he have tested if trigger filter have effect but if I understand right trigger hysteresis change did not. Also changing ADC mode from interleaved to non interleaved did not affect.
Also just this particular trigger type many conditions must be met, much more complex than some simplest possible edge trig.
If it make error and do not trig.. btw... it have made this error. We have seen it in every image. So this need keep carefully in thinking logic.
It need think. Every time it have "trigged" wrong place... we really do not even know if it is trigged... but other thing we know sure... every this fail image we see part of signal what meet all needs for trig and it have not trigged or least positioned it to right place... what is also important to keep in mind.
How we know it is trigged just there where is trigger time position and signal position is wrong. Think again... who ever is thinking this... how we know it IS trigged just in this position where trigger mark is and we see this signal in wrong position in case it have failed. Who know... I do not know and trigger do not tell what and when she have done things