It's 2019 and I too have this swimming issue... again!
Maybe they need another year? Or maybe "they're just pissing on us without even giving us the courtesy of calling it rain."
February 2019 - last edited February 2019
Releasing W when stalling, and then hitting escape for a few seconds, then swimming again got me through this.
Man... super glad I didn't spend any appreciable money for this game...
2019 and the issue still hasn't been fixed. I managed to get through though by alternating between sprint and pause, finally got my way through after 5 minutes. Hope that helps!