@Ernest BywaterI have a dozen to twenty readers who consistently report errors or discrepancies when I post a chapter. A couple more from Fine Stories.
I am happy when I have 3 or fewer errors in a chapter of 10,000 to 12,000 words. Typically, I have six to a dozen errors, or more. Thanks to my volunteer proofreader I have fewer errors. If I were to decide to publish a print or ebook, I would have to get an editor!
Locally there are 3 or 4 writers who post on SOL, and a couple of readers; several of whom I see on weekly, or at least monthly. I sometimes get a text about suggested corrections before I get the email notifying me about my current chapter getting posted.
When I first started posting most of the suggested corrections were made by multiple people. After posting some 20 chapters I have improved as a writer. I make fewer obvious errors. So, recently I have found that similar to what Ernest Bywater commented, each person that PMs me has noticed different errors.
Part of this is because some people who PM me notice particular things. I suspect that some differences are because of how people read it, and the resolution.
I don't have internet where I live, so, like now I'm using my phone. The chapters display differently than when reading on my laptop. Both are different from MS Word.
When possible, I try to read my recent postings on my laptop, then on my phone. I often catch different errors.
If they are glaring errors, I correct my master document, then upload the corrections ASAP. Otherwise, I tend to wait 1 to 2 weeks, checking Fine Storiesonline.net too. Although I make the corrections, and save on a version x.1 document.
I respond to All PMs, even if I don't make a correction. Sometimes it is less an error than an opinion. Or, I have a character "miss-speaking" for a reason. Occasionally, it is differences between USA, English, Australian, or a regional dialect; or manner of speaking.
Sometimes it is because I am using the US Army (or USMC, USAF, etc.) "Style Guide" or military slang or vernacular. Not all of my readers appreciate my using this style. I do consider those comments. I decided that I am trying to "Show not Tell" also, I am annoyed when movies or books "get it wrong" although, that is subjective.
I really do appreciate people who PM me about my story. Corrections, suggestions, and comments. I consider what they say. If I don't agree, I still respond, thank them. Often I offer my reasoning. Sometimes an exchange of PMs may result in one or both of us modifying our opinions.
Back to the OP, the better you write, the less likely that multiple people will notify us about the same error. Partially because of how the chapters display on different devices. Partially because not as many people will notice an error that is not glaring.
Also, readers who follow a particular writer may be less likely to notice some errors, thinking "that's just that writer's style." Or, Ernest Bywater is using Australian English.
I recognized that another writer on SOL was South African by cues in their writing, before it was confirmed in the story that it was set in South Africa.
I enjoy languages, and the subtle (or not) differences between a Geordie, a Yorkshire dialect, a Welshman, Scot, Texan, Georgian, or New Yorker; Berliners, Silesians, and Bavarian. I get some comments that use of dialect, slang, and foreign languages in particular "take some people out of the story"
For me, I find it odd if a story set in Louisiana or Georgia is written in plain English. I grew up reading Mark Twain, and Robert Service. Later Louis L'Amour, so reading in dialect and different languages is part of the joy of immersive reading (and traveling).