Recently tried to use 3G modem Pantech UML290 with LEDE 17.01.5 and fount that chat can't execute the connection script with it any more. Exactly the same script and configuration works for OpenWRT 15.05.1, but fails here:
Tue Aug 14 17:44:21 2018 local2.info chat[5238]: abort on (BUSY)
Tue Aug 14 17:44:21 2018 local2.info chat[5238]: abort on (NO CARRIER)
Tue Aug 14 17:44:21 2018 local2.info chat[5238]: abort on (ERROR)
Tue Aug 14 17:44:21 2018 local2.info chat[5238]: report (CONNECT)
Tue Aug 14 17:44:21 2018 local2.info chat[5238]: timeout set to 10 seconds
Tue Aug 14 17:44:21 2018 local2.info chat[5238]: send (AT&F^M)
Tue Aug 14 17:44:21 2018 local2.info chat[5238]: expect (OK)
Tue Aug 14 17:44:21 2018 local2.info chat[5238]: AT&F^M^M
Tue Aug 14 17:44:21 2018 local2.info chat[5238]: OK
Tue Aug 14 17:44:21 2018 local2.info chat[5238]: -- got it
Tue Aug 14 17:44:21 2018 local2.info chat[5238]: send (ATE1^M)
Tue Aug 14 17:44:21 2018 local2.info chat[5238]: expect (OK)
Tue Aug 14 17:44:21 2018 local2.info chat[5238]: ^M
Tue Aug 14 17:44:21 2018 local2.info chat[5238]: ^M
Tue Aug 14 17:44:21 2018 local2.info chat[5238]: OK
Tue Aug 14 17:44:21 2018 local2.info chat[5238]: -- got it
Tue Aug 14 17:44:21 2018 local2.info chat[5238]: send (AT+CGDCONT=1,"IP","internet"^M)
Tue Aug 14 17:44:21 2018 local2.info chat[5238]: timeout set to 30 seconds
Tue Aug 14 17:44:21 2018 local2.info chat[5238]: expect (OK)
Tue Aug 14 17:44:21 2018 local2.info chat[5238]: ^M
Tue Aug 14 17:44:21 2018 local2.info chat[5238]: AT+CGDCONT=1,"IP","internet"^M^M
Tue Aug 14 17:44:21 2018 local2.info chat[5238]: OK
Tue Aug 14 17:44:21 2018 local2.info chat[5238]: -- got it
Tue Aug 14 17:44:21 2018 local2.info chat[5238]: send (ATD*99***1#^M)
Tue Aug 14 17:44:21 2018 local2.info chat[5238]: expect (CONNECT)
Tue Aug 14 17:44:21 2018 local2.info chat[5238]: ^M
Tue Aug 14 17:44:21 2018 local2.info chat[5238]: ATD*99***1#^M^M
Tue Aug 14 17:44:21 2018 local2.info chat[5238]: NO CARRIER
Tue Aug 14 17:44:21 2018 local2.info chat[5238]: -- failed
Tue Aug 14 17:44:21 2018 local2.info chat[5238]: Failed (NO CARRIER)
Tue Aug 14 17:44:21 2018 daemon.err pppd[5236]: Connect script failed
Tue Aug 14 17:44:22 2018 daemon.info pppd[5236]: Exit.
Tue Aug 14 17:44:22 2018 daemon.notice netifd: Interface 'modem' is now down
The same configuration for OpenWRT 15.05.1:
Aug 14 18:11:33 TEST local2.info chat[5460]: abort on (BUSY)
Aug 14 18:11:33 TEST local2.info chat[5460]: abort on (NO CARRIER)
Aug 14 18:11:33 TEST local2.info chat[5460]: abort on (ERROR)
Aug 14 18:11:33 TEST local2.info chat[5460]: report (CONNECT)
Aug 14 18:11:33 TEST local2.info chat[5460]: timeout set to 10 seconds
Aug 14 18:11:33 TEST local2.info chat[5460]: send (AT&F^M)
Aug 14 18:11:33 TEST local2.info chat[5460]: expect (OK)
Aug 14 18:11:33 TEST local2.info chat[5460]: AT&F^M^M
Aug 14 18:11:33 TEST local2.info chat[5460]: OK
Aug 14 18:11:33 TEST local2.info chat[5460]: -- got it
Aug 14 18:11:33 TEST local2.info chat[5460]: send (ATE1^M)
Aug 14 18:11:33 TEST local2.info chat[5460]: expect (OK)
Aug 14 18:11:33 TEST local2.info chat[5460]: ^M
Aug 14 18:11:33 TEST local2.info chat[5460]: ^M
Aug 14 18:11:33 TEST local2.info chat[5460]: OK
Aug 14 18:11:33 TEST local2.info chat[5460]: -- got it
Aug 14 18:11:33 TEST local2.info chat[5460]: send (AT+CGDCONT=1,"IP","internet"^M)
Aug 14 18:11:33 TEST local2.info chat[5460]: timeout set to 30 seconds
Aug 14 18:11:33 TEST local2.info chat[5460]: expect (OK)
Aug 14 18:11:33 TEST local2.info chat[5460]: ^M
Aug 14 18:11:33 TEST local2.info chat[5460]: AT+CGDCONT=1,"IP","internet"^M^M
Aug 14 18:11:33 TEST local2.info chat[5460]: OK
Aug 14 18:11:33 TEST local2.info chat[5460]: -- got it
Aug 14 18:11:33 TEST local2.info chat[5460]: send (ATD*99***1#^M)
Aug 14 18:11:33 TEST local2.info chat[5460]: expect (CONNECT)
Aug 14 18:11:33 TEST local2.info chat[5460]: ^M
Aug 14 18:11:33 TEST local2.info chat[5460]: ATD*99***1#^M^M
Aug 14 18:11:33 TEST local2.info chat[5460]: CONNECT
Aug 14 18:11:33 TEST local2.info chat[5460]: -- got it
Aug 14 18:11:33 TEST local2.info chat[5460]: send ( ^M)
Aug 14 18:11:33 TEST daemon.info pppd[5422]: Serial connection established.
Aug 14 18:11:33 TEST daemon.info pppd[5422]: Using interface 3g-wan
Aug 14 18:11:33 TEST daemon.notice pppd[5422]: Connect: 3g-wan <--> /dev/ttyACM0
Aug 14 18:11:34 TEST daemon.info pppd[5422]: CHAP authentication succeeded
Aug 14 18:11:34 TEST daemon.notice pppd[5422]: CHAP authentication succeeded
Aug 14 18:11:37 TEST daemon.warn pppd[5422]: Could not determine remote IP address: defaulting to 10.64.64.64
Aug 14 18:11:37 TEST daemon.notice pppd[5422]: local IP address 10.168.84.72
Aug 14 18:11:37 TEST daemon.notice pppd[5422]: remote IP address 10.64.64.64
Looks like a bug. Can anyone suggest how to investigate the source of the problem?