Добавил debug к pppd опциям, получил такой лог:
Jan 1 03:00:04 pppd[61]: pppd 2.4.2 started by (unknown), uid 0
Jan 1 03:00:04 pppd[61]: Serial connection established.
Jan 1 03:00:04 pppd[61]: using channel 1
Jan 1 03:00:04 pppd[61]: Using interface ppp0
Jan 1 03:00:04 pppd[61]: Connect: ppp0 <--> /dev/pts/0
Jan 1 03:00:05 pppd[61]: sent [LCP ConfReq id=0x1 <magic 0xdc74c694>]
Jan 1 03:00:08 pppd[61]: sent [LCP ConfReq id=0x1 <magic 0xdc74c694>]
Jan 1 03:00:11 pppd[61]: sent [LCP ConfReq id=0x1 <magic 0xdc74c694>]
Jan 1 03:00:14 pppd[61]: sent [LCP ConfReq id=0x1 <magic 0xdc74c694>]
Jan 1 03:00:16 udhcpd: sending OFFER of 192.168.1.2
Jan 1 03:00:16 udhcpd: sending ACK to 192.168.1.2
Jan 1 03:00:17 pppd[61]: sent [LCP ConfReq id=0x1 <magic 0xdc74c694>]
Jan 1 03:00:20 pppd[61]: sent [LCP ConfReq id=0x1 <magic 0xdc74c694>]
Jan 1 03:00:23 pppd[61]: sent [LCP ConfReq id=0x1 <magic 0xdc74c694>]
Jan 1 03:00:26 pppd[61]: sent [LCP ConfReq id=0x1 <magic 0xdc74c694>]
Jan 1 03:00:29 pppd[61]: sent [LCP ConfReq id=0x1 <magic 0xdc74c694>]
Jan 1 03:00:32 pppd[61]: sent [LCP ConfReq id=0x1 <magic 0xdc74c694>]
Jan 1 03:00:35 pppd[61]: LCP: timeout sending Config-Requests
Jan 1 03:00:35 pppd[61]: Connection terminated.
Jan 1 03:01:06 pppd[61]: Serial connection established.
Jan 1 03:01:06 pppd[61]: using channel 2
Jan 1 03:01:06 pppd[61]: Using interface ppp0
Jan 1 03:01:06 pppd[61]: Connect: ppp0 <--> /dev/pts/1
Jan 1 03:01:07 pptp[154]: Call manager for 10.0.4.1 is already running.
Jan 1 03:01:07 pptp[154]: Could not open unix socket for 10.0.4.1
Jan 1 03:01:07 pppd[61]: Script /usr/sbin/pptp 10.0.4.1 --nolaunchpppd --nobuffer --sync finished (pid 148), status = 0x1
Jan 1 03:01:07 pppd[61]: Modem hangup
Jan 1 03:01:07 pppd[61]: Connection terminated.
Jan 1 03:01:07 pptp[149]: Call manager exited with error 256
Jan 1 03:01:37 pppd[61]: Serial connection established.
Jan 1 03:01:37 pppd[61]: using channel 3
Jan 1 03:01:37 pppd[61]: Using interface ppp0
Jan 1 03:01:37 pppd[61]: Connect: ppp0 <--> /dev/pts/1
Jan 1 03:01:38 pptp[197]: Call manager for 10.0.4.1 is already running.
Jan 1 03:01:38 pptp[197]: Could not open unix socket for 10.0.4.1
Jan 1 03:01:38 pptp[192]: Call manager exited with error 256
Jan 1 03:01:38 pppd[61]: Script /usr/sbin/pptp 10.0.4.1 --nolaunchpppd --nobuffer --sync finished (pid 191), status = 0x1
Jan 1 03:01:38 pppd[61]: Modem hangup
Jan 1 03:01:38 pppd[61]: Connection terminated.
Jan 1 03:02:08 pppd[61]: Serial connection established.
Jan 1 03:02:08 pppd[61]: using channel 4
Jan 1 03:02:08 pppd[61]: Using interface ppp0
Jan 1 03:02:08 pppd[61]: Connect: ppp0 <--> /dev/pts/1
Jan 1 03:02:08 pptp[240]: Call manager for 10.0.4.1 is already running.
Jan 1 03:02:08 pptp[240]: Could not open unix socket for 10.0.4.1
Jan 1 03:02:08 pptp[235]: Call manager exited with error 256
Jan 1 03:02:08 pppd[61]: Script /usr/sbin/pptp 10.0.4.1 --nolaunchpppd --nobuffer --sync finished (pid 234), status = 0x1
Jan 1 03:02:08 pppd[61]: Modem hangup
Jan 1 03:02:08 pppd[61]: Connection terminated.
Jan 1 03:02:39 pppd[61]: Serial connection established.
Jan 1 03:02:39 pppd[61]: using channel 5
Jan 1 03:02:39 pppd[61]: Using interface ppp0
Jan 1 03:02:39 pppd[61]: Connect: ppp0 <--> /dev/pts/1
Jan 1 03:02:40 pppd[61]: sent [LCP ConfReq id=0x2 <magic 0x7887a12c>]
Jan 1 03:02:41 pptp[285]: Call manager for 10.0.4.1 is already running.
Jan 1 03:02:41 pptp[285]: Could not open unix socket for 10.0.4.1
Jan 1 03:02:41 pppd[61]: Script /usr/sbin/pptp 10.0.4.1 --nolaunchpppd --nobuffer --sync finished (pid 66), status = 0x1
Jan 1 03:02:41 pptp[71]: Call manager exited with error 256
Jan 1 03:02:43 pppd[61]: sent [LCP ConfReq id=0x2 <magic 0x7887a12c>]
Jan 1 03:02:46 pppd[61]: sent [LCP ConfReq id=0x2 <magic 0x7887a12c>]
Jan 1 03:02:49 pppd[61]: sent [LCP ConfReq id=0x2 <magic 0x7887a12c>]
Jan 1 03:02:52 pppd[61]: sent [LCP ConfReq id=0x2 <magic 0x7887a12c>]
Jan 1 03:02:55 pppd[61]: sent [LCP ConfReq id=0x2 <magic 0x7887a12c>]
Jan 1 03:02:58 pppd[61]: sent [LCP ConfReq id=0x2 <magic 0x7887a12c>]
Jan 1 03:03:01 pppd[61]: sent [LCP ConfReq id=0x2 <magic 0x7887a12c>]
Jan 1 03:03:04 pppd[61]: sent [LCP ConfReq id=0x2 <magic 0x7887a12c>]
Jan 1 03:03:07 pppd[61]: sent [LCP ConfReq id=0x2 <magic 0x7887a12c>]
Jan 1 03:03:10 pppd[61]: LCP: timeout sending Config-Requests
Jan 1 03:03:10 pppd[61]: Connection terminated.
Что ещё можно сделать или посмотреть?