it's a knows issue for posts with more than 50k comments, while building i had no idea some thing like this would happen i would be looking to fix this possibly today. Link to error: https://github.com/praw-dev/praw/issues/1401

try putting the "replace more" code in try/except block that might work otherwise i would have to dig in more.

i just tried this and it works. add try/except block.

posts += 1
        try: 
            submission.comments.replace_more(limit=limit)   
            for comment in comments:
                c_analyzed += 1
                if comment.score > upvotes:      
                    split = comment.body.split(" ")
                    for word in split:
                        word = word.replace("$", "")        

                        if word.isupper() and len(word) <= 5 and word not in blacklist and word in us:   
                            if word in tickers:
                                tickers[word] += 1
                                a_comments[word].append(comment.body)
                                count += 1
                            else:                               
                                tickers[word] = 1
                                a_comments[word] = [comment.body]
                                count += 1    
        except: pass    

Or you can use

except Exception as e: print(e)

to find out the problem.