OPTIMIZE INDEX - something wrong

I have some problem with OPTIMIZE INDEX.

I call
optimize index prod_addr_v2

Then i call
show threads

It shows than optimize thread is started:
| 100172 | - | - | | 2.671889 | SYSTEM OPTIMIZE |

Then i look in index directoy. I see 3 new files:
-rw------- 1 _sphinx _sphinx 262140 22 feb. 17:06 prod_addr_v2.1.tmp.spa
-rw------- 1 _sphinx _sphinx 0 22 feb. 17:06 prod_addr_v2.1.tmp.spm
-rw------- 1 _sphinx _sphinx 0 22 feb. 17:06 prod_addr_v2.1.tmp.sps

And nothing else happen. I waited for many hours, repeat after manticore reboot, after server reboot…
top doesn’t show any load on my server - no CPU usage, no IO usage. No parameters in config that limit resource usage for optimize.

How can i fight with this promblem?

Manticore 2.7.5 on FreeBSD 11.2-RELEASE-p4.

could you reproduce issue with daemon run with —logdebug option? or provide BT from hung daemon?

Daemon is not hanging - it works, accept connections, response on requests.

There is crash info with --logedbug

[Fri Feb 22 18:02:37.288 2019] [100290] DEBUG: progressive merge - merging 1 (179801 kb) with 2 (2 kb)
------- FATAL: CRASH DUMP -------
[Fri Feb 22 18:02:37.071 2019] [27876]

--- crashed invalid query ---

--- request dump end ---
Manticore 2.7.5 4a31c54@181204 release
Handling signal 11
-------------- backtrace begins here ---------------
Program compiled with 4.2.1
Configured with flags: Configured by CMake with these definitions: -DCMAKE_BUILD_TYPE=RelWithDebInfo -DDL_EXPAT=1 -DEXPAT_LIB=libexpat.so.1 -DUSE_LIBICONV=1 -DDL_MYSQL=1 -DMYSQL_LIB=libmysqlclient.so.21 -DDATADIR=/usr/local/var/data -DUSE_BISON=ON -DUSE_FLEX=ON -DUSE_SYSLOG=1 -DWITH_EXPAT=ON -DWITH_ICONV=ON -DWITH_MYSQL=1 -DWITH_ZLIB=ON
Host OS is FreeBSD test.instella.com 11.2-RELEASE-p4 FreeBSD 11.2-RELEASE-p4 #0: Thu Sep 27 08:16:24 UTC 2018     root@amd64-builder.daemonology.net:/usr/obj/usr/src/sys/GENERIC  amd64
Stack bottom = 0x7fffdf9f179f, thread stack size = 0x100000
Trying manual backtrace:
Something wrong with thread stack, manual backtrace may be incorrect (fp=0x7fffdf9f02b0)
Stack looks OK, attempting backtrace.
Something wrong in frame pointers, manual backtrace failed (fp=0)
-------------- backtrace ends here ---------------
--- BT to source lines (depth 0): ---
--- BT to source lines finished ---
--- 2 active threads ---
thd 0, proto sphinxql, state handshake, command SYSTEM
thd 1, proto sphinxql, state handshake, command SYSTEM
------- CRASH DUMP END -------

As it is crash, i create bug report