Campaigns not working

[robson]

My email campaigns stopped working after migrating from PHP7.0 to 7.1 Test emails work. Errors are generated both on my own email server and GMAIL (on both test emails are working)
Here is log: https://pastebin.com/embed_iframe/0sduJRVw

Mail server reports (I can only check my own):
6/19/2019, 12:58:03 AM info imap-login: Disconnected (no auth attempts in 0 secs): user=<>, rip=195.181.209.217, lip=172.22.1.8, TLS handshaking: SSL_accept() failed: error:14094418:SSL routines:ssl3_read_bytes:tlsv1 alert unknown ca: SSL alert number 48
6/19/2019, 12:58:03 AM info imap-login: Disconnected (no auth attempts in 0 secs): user=<>, rip=195.181.209.217, lip=172.22.1.8, TLS handshaking: SSL_accept() failed: error:14094418:SSL routines:ssl3_read_bytes:tlsv1 alert unknown ca: SSL alert number 48
6/19/2019, 12:58:03 AM info imap-login: Disconnected (no auth attempts in 1 secs): user=<>, rip=195.181.209.217, lip=172.22.1.8, TLS handshaking: SSL_accept() failed: error:14094418:SSL routines:ssl3_read_bytes:tlsv1 alert unknown ca: SSL alert number 48
6/19/2019, 12:58:02 AM info imap-login: Disconnected (no auth attempts in 0 secs): user=<>, rip=195.181.209.217, lip=172.22.1.8, TLS handshaking: SSL_accept() failed: error:14094418:SSL routines:ssl3_read_bytes:tlsv1 alert unknown ca: SSL alert number 48

I just want to be clear that both gmail and my own mailserver send test emails from Espo, however they cannot send Mass Mailings within Campaign. All happened upon migration to PHP7.1 so it has to be the reason!!!!
[2019-06-19 00:53:03] Espo.ERROR: CronManager: Failed job running, job [5d0986f5c5a6fbedb]. Error Details: Job CheckEmailAccounts 5b505a31662e79556: [0] cannot connect to host ; error = fsockopen(): unable to connect to ssl://mail.crm.com:993 (Unknown error) (errno = 0 ) [] []

[2019-06-19 00:56:04] Espo.ERROR: CronManager: Failed job running, job [5d0986ba312a505fd]. Error Details: Job CheckInboundEmails 5d0975b6e67319738: [0] cannot connect to host ; error = fsockopen(): unable to connect to ssl://imap.gmail.com:993 (Unknown error) (errno = 0 ) [] []

Especially this one: [2019-06-19 00:35:03] Espo.ERROR: MassEmail#sendQueueItem: [0] Content must be string or resource; received "boolean" [] []
Looks like an error in the code. Heard that migration to php7.1 created some issues with strings...

and this one:
[2019-06-19 00:10:04] Espo.WARNING: E_WARNING: stream_socket_enable_crypto(): SSL operation failed with code 1. OpenSSL Error messages: error:1416F086:SSL routines:tls_process_server_certificate:certificat e verify failed {"code":2,"message":"stream_socket_enable_crypt o() : SSL operation failed with code 1. OpenSSL Error messages:\nerror:1416F086:SSL routines:tls_process_server_certificate:certificat e verify failed","file":"/var/www/public_html/vendor/zendframework/zend-mail/src/Protocol/Smtp.php","line":215,"context":{"host":"crm.com"}} []

and this one: https://pastebin.com/embed_js/fcW3zUVa