Why is the SSH tunnel unstable?

Question

SSH

I wanted to access my Raspberry Pi on my home network from the outside world. To do this, I decided to use a server from DigitalOcean.
on Raspberry Pi:

autossh -f -N [email protected] -R 3700:192.168.1.xx:22

(Password from DO is not requested, because there are SSH keys)
on the DigitalOcean server:

ssh [email protected] -p3700

Sometimes I get access to Raspberry, sometimes I don't. I don't understand what's the matter.