My first thought was the max clients setting and the IP range you're giving pptp to give out to clients. Have you checked both of these settings?

This might also be helpful in enabling some debugging logs to start looking for why the new connections aren't accepted after you reach 47.

I checked max clients (default value is 100 - changed it to 2000).
Remoteip settings looks like that: 172.16.0.2-254,172.16.1.2-254,172.16.2.2-254,172.16.3.2-254
So this shouldn't be a problem.

Log for single client looks like that:

Nov 29 10:18:09 DeimicVPN pptpd[3705]: CTRL: Client xx.xx.xx.xx control connection started
Nov 29 10:18:10 DeimicVPN pptpd[3705]: CTRL: Starting call (launching pppd, opening GRE)
Nov 29 10:18:10 DeimicVPN pppd[3706]: Plugin /usr/lib/pptpd/pptpd-logwtmp.so loaded.
Nov 29 10:18:10 DeimicVPN pppd[3706]: pptpd-logwtmp: $Version$
Nov 29 10:18:10 DeimicVPN pppd[3706]: pppd 2.4.6 started by root, uid 0
Nov 29 10:18:10 DeimicVPN pppd[3706]: using channel 181
Nov 29 10:18:41 DeimicVPN pptpd[3705]: CTRL: Reaping child PPP[3706]

It always takes ~30 seconds to kill the client

EDIT:

lcp-echo-interval 30
lcp-echo-failure 4

Also got this options set in configuration