astpp stuck after 200 concurrent calls or more

those are some logs once problem is present:

2020-01-14 18:22:58.014930 [ERR] switch_core_sqldb.c:587 NATIVE SQL ERR [unable to open database file]
2020-01-14 18:22:58.014930 [DEBUG] switch_cpp.cpp:1365 [ASTPP] [GET_OVERRIDE_CALLERID] Query :SELECT callerid_name as cid_name,callerid_number as cid_number,accountid FROM accounts_callerid WHERE accountid = 110 AND status=0 LIMIT 1
752c2d8a-36f2-11ea-8ae6-dd6cf8c94168 2020-01-14 18:22:58.014930 [ERR] mod_json_cdr.c:396 Got error [0] posting to web server [http://localhost:8735/cdr.php]
752c2d8a-36f2-11ea-8ae6-dd6cf8c94168 2020-01-14 18:22:58.014930 [ERR] mod_json_cdr.c:415 Unable to post to web server
752c2d8a-36f2-11ea-8ae6-dd6cf8c94168 2020-01-14 18:22:58.014930 [ERR] mod_json_cdr.c:232 Can't open /usr/share/freeswitch/log/xml_json/752c2d8a-36f2-11ea-8ae6-dd6cf8c94168.cdr.json! [Too many open files]
7db77040-36f2-11ea-95de-dd6cf8c94168 2020-01-14 18:22:58.014930 [ERR] switch_core_media.c:7567 AUDIO RTP REPORTS ERROR: [Socket Error!]
2020-01-14 18:22:58.014930 [ERR] switch_core_sqldb.c:587 NATIVE SQL ERR [unable to open database file]
2020-01-14 18:22:58.014930 [ERR] switch_core_sqldb.c:587 NATIVE SQL ERR [unable to open database file]
7ffd0fc2-36f2-11ea-997c-dd6cf8c94168 2020-01-14 18:22:58.034923 [ERR] mod_json_cdr.c:396 Got error [0] posting to web server [http://localhost:8735/cdr.php]
7ffd0fc2-36f2-11ea-997c-dd6cf8c94168 2020-01-14 18:22:58.034923 [ERR] mod_json_cdr.c:415 Unable to post to web server
7ffd0fc2-36f2-11ea-997c-dd6cf8c94168 2020-01-14 18:22:58.034923 [ERR] mod_json_cdr.c:232 Can't open /usr/share/freeswitch/log/xml_json/7ffd0fc2-36f2-11ea-997c-dd6cf8c94168.cdr.json! [Too many open files]
7db77040-36f2-11ea-95de-dd6cf8c94168 2020-01-14 18:22:58.034923 [ERR] mod_json_cdr.c:396 Got error [0] posting to web server [http://localhost:8735/cdr.php]
7db77040-36f2-11ea-95de-dd6cf8c94168 2020-01-14 18:22:58.034923 [ERR] mod_json_cdr.c:415 Unable to post to web server
7db77040-36f2-11ea-95de-dd6cf8c94168 2020-01-14 18:22:58.034923 [ERR] mod_json_cdr.c:232 Can't open /usr/share/freeswitch/log/xml_json/7db77040-36f2-11ea-95de-dd6cf8c94168.cdr.json! [No such file or directory]

obviously my ulimit parameters are following:

ulimit -c unlimited # The maximum size of core files created.
ulimit -d unlimited # The maximum size of a process's data segment.
ulimit -f unlimited # The maximum size of files created by the shell (default option)
ulimit -i unlimited # The maximum number of pending signals
ulimit -n 999999 # The maximum number of open file descriptors.
ulimit -q unlimited # The maximum POSIX message queue size
ulimit -u unlimited # The maximum number of processes available to a single user.
ulimit -v unlimited # The maximum amount of virtual memory available to the process.
ulimit -x unlimited # ???
ulimit -s 240 # The maximum stack size
ulimit -l unlimited # The maximum size that may be locked into memory.
ulimit -a # All current limits are reported.

when problem happens, it is needed to restart freeswitch process with service freeswitch restart on centos 7.7.

someone have had same problem but for now no solution: https://groups.google.com/forum/#!topic/astpp/zg5usqTvHtQ

any suggestion?