Anyone experiencing greater difficulty in later rounds?

I just did a run in the zarya cosmodrone to get to round 50. I did it over multiple days so I saved and quit for next day. I dont know if that contributes to anything cause explosions dont occur from grenades or the ray gun. My guns dont show level any more. So I dont know if this contributes to the next part but the zombies hit pretty hard and spawn crazy fast. There's no training cause any time I run from one side to the other I already have 4 right in my pathing. Maybe its the size of the map being a lot smaller than 115 so zombies just spawn from everywhere but it was a scrape just to get to round 51 for the gobblegum.