Some important things to note
There's a difference between stranger missions, stranger dialogues, stranger ongoing events, random encounters, and quests.
For example, a stranger mission series is indicated by a question mark or letters in a white zone on the map. These are missable and time-sensitive. Some of these optional missions arise from camp members. Some are unlocked at only set chapters, some have prerequisites, some only open at set honor ranks.
A random encounter is a white dot echo on the map, and some/many of these respawn or reoccur.
stranger dialogues are when you have non-mission interactions with weirdoes across the map. They are usually multiple staged and change post epilogue. In that sense they are time-sensitive.
ongoing events, like the home building, follow set time/place patterns and you can either join in at that time, or at a later stage (it will be different), or miss them. It's hard to do all theses without knowing them in advance.
some camp member item requests are only available at certain chapters after certain interactions - like playing poker with person X during chapter 3 - they are easily missable.
easter eggs vary between places of special interest, unique items, unique documents, and time-sensitive events (being a certain place and time).
These are random events that occur all over RDR2 in a way to give a feeling of more life. My understanding is if you complete a chance encounter and it's successful then the encounter will not occur again.
If you fail a random encounter then the encounter will "respawn" and have a chance to be completed again. There doesn't seem to be a defined time for these to happen, most likely the best thing to do is go to another part of the map and pass a few in-game days, once you've passed them you can go back and look to trigger the chance encounter.
I'm unsure what exactly your situation falls under but this should hopefully help.