Reddit won't let me post the video and photo together, but I recently found more webs in GTA 5s prologue and I believe a web can be found in the cutscene after the train hits the car. I uploaded another post with a video showing the other webs. In total I've found 9 in the prologue.
So I've been enthralled by the spiderweb mystery recently much like most people in the community. I decided to go back over old mysteries, and pieces of the puzzle that went cold when they were initially found. 10 years ago a spiderweb texture was found in north yankton both in the prologue and bury the hatchet. However due to the texture being called sewer grate in the text files, as well as it being found on all the rocks next to the frozen alien, it was dismissed as being a texture glitch. But with the recent findings of the 9 webs in RDR2 on the electrical poles, and the spider webs found on Mount Chilliad being made from electrical wires, I had a feeling we were missing something. Combing over the prologue I was able to find more spiderwebs, I've found a total of 9 spider webs so far, matching the 9 found in rdr2. Most interesting to me tho is it appears one of the webs actually appears in the cutscene right after the train hits the car. I've attached video to show my findings, hope this helps the hunt.
Edit: It should be mentioned that YouTuber Whizl released a video showcasing that these spiders webs near the bank glow green(currently undiscovered how to activate in game), whereas the webs on the rock do not. Meaning rockstar intentionally altered the code to be uniquely different.
Comparing the size of sewer grates from story mode compared to north Yankton reveals a good size difference between the two. Not to mention the only time this specific "sewer grate" texture is used is in north yankton.