I don't think the problem is related to the charset, the server has been standing for several years and has never presented problems with any file or folder. The same identical problem has also started to occur on another server. The error also occurs during the night when nobody works on the files. Today, looking at the logs, I found this information, I hope they can help you:
[2019/05/22 07:59:18.682017, 0] ../source3/smbd/negprot.c:566(reply_negprot) negprot protocols not 0-terminated [2019/05/22 07:59:18.758200, 0] ../lib/util/fault.c:78(fault_report) =============================================================== [2019/05/22 07:59:18.758224, 0] ../lib/util/fault.c:79(fault_report) INTERNAL ERROR: Signal 11 in pid 10659 (4.5.16-Debian) Please read the Trouble-Shooting section of the Samba HOWTO [2019/05/22 07:59:18.758235, 0] ../lib/util/fault.c:81(fault_report) =============================================================== [2019/05/22 07:59:18.758243, 0] ../source3/lib/util.c:791(smb_panic_s3) PANIC (pid 10659): internal error [2019/05/22 07:59:18.758634, 0] ../source3/lib/util.c:902(log_stack_trace) BACKTRACE: 25 stack frames: #0 /usr/lib/x86_64-linux-gnu/libsmbconf.so.0(log_stack_trace+0x1c) [0x7f7321882c0c] #1 /usr/lib/x86_64-linux-gnu/libsmbconf.so.0(smb_panic_s3+0x20) [0x7f7321882ce0] #2 /usr/lib/x86_64-linux-gnu/libsamba-util.so.0(smb_panic+0x2f) [0x7f7323d9f19f] #3 /usr/lib/x86_64-linux-gnu/libsamba-util.so.0(+0x1b3b6) [0x7f7323d9f3b6] #4 /lib/x86_64-linux-gnu/libpthread.so.0(+0x110e0) [0x7f73240090e0] #5 /usr/lib/x86_64-linux-gnu/samba/libsmbd-base.so.0(smbXsrv_session_create+0x2b) [0x7f732399177b] #6 /usr/lib/x86_64-linux-gnu/samba/libsmbd-base.so.0(reply_sesssetup_and_X+0x967) [0x7f7323925a17] #7 /usr/lib/x86_64-linux-gnu/samba/libsmbd-base.so.0(+0x123086) [0x7f7323963086] #8 /usr/lib/x86_64-linux-gnu/samba/libsmbd-base.so.0(+0x1254ba) [0x7f73239654ba] #9 /usr/lib/x86_64-linux-gnu/samba/libsmbd-base.so.0(+0x1264ac) [0x7f73239664ac] #10 /usr/lib/x86_64-linux-gnu/libtevent.so.0(+0xaea3) [0x7f73204c3ea3] #11 /usr/lib/x86_64-linux-gnu/libtevent.so.0(+0x9277) [0x7f73204c2277] #12 /usr/lib/x86_64-linux-gnu/libtevent.so.0(_tevent_loop_once+0x9d) [0x7f73204be04d] #13 /usr/lib/x86_64-linux-gnu/libtevent.so.0(tevent_common_loop_wait+0x1b) [0x7f73204be27b] #14 /usr/lib/x86_64-linux-gnu/libtevent.so.0(+0x9217) [0x7f73204c2217] #15 /usr/lib/x86_64-linux-gnu/samba/libsmbd-base.so.0(smbd_process+0x6c9) [0x7f73239677d9] #16 /usr/sbin/smbd(+0xa7b4) [0x56342e4627b4] #17 /usr/lib/x86_64-linux-gnu/libtevent.so.0(+0xaea3) [0x7f73204c3ea3] #18 /usr/lib/x86_64-linux-gnu/libtevent.so.0(+0x9277) [0x7f73204c2277] #19 /usr/lib/x86_64-linux-gnu/libtevent.so.0(_tevent_loop_once+0x9d) [0x7f73204be04d] #20 /usr/lib/x86_64-linux-gnu/libtevent.so.0(tevent_common_loop_wait+0x1b) [0x7f73204be27b] #21 /usr/lib/x86_64-linux-gnu/libtevent.so.0(+0x9217) [0x7f73204c2217] #22 /usr/sbin/smbd(main+0x1784) [0x56342e45f4f4] #23 /lib/x86_64-linux-gnu/libc.so.6(__libc_start_main+0xf1) [0x7f732013a2e1] #24 /usr/sbin/smbd(_start+0x2a) [0x56342e45f5fa] [2019/05/22 07:59:18.758708, 0] ../source3/lib/util.c:803(smb_panic_s3) smb_panic(): calling panic action [/usr/share/samba/panic-action 10659] 29 ../sysdeps/unix/sysv/linux/waitpid.c: File o directory non esistente. [2019/05/22 07:59:19.495423, 0] ../source3/lib/util.c:811(smb_panic_s3) smb_panic(): action returned status 0 [2019/05/22 07:59:19.495463, 0] ../source3/lib/dumpcore.c:303(dump_core) dumping core in /var/log/samba/cores/smbd These are the latest updated packages, Is it possible that the problem is related to one of these? [INSTALL, DEPENDENCIES] linux-image-4.9.0-9-amd64:amd64 4.9.168-1 [UPGRADE] base-files:amd64 9.9+deb9u8 -> 9.9+deb9u9 [UPGRADE] libjs-bootstrap:amd64 3.3.7+dfsg-2+deb9u1 -> 3.3.7+dfsg-2+deb9u2 [UPGRADE] libjs-jquery:amd64 3.1.1-2 -> 3.1.1-2+deb9u1 [UPGRADE] libmariadbclient18:amd64 10.1.37-0+deb9u1 -> 10.1.38-0+deb9u1 [UPGRADE] libpng16-16:amd64 1.6.28-1 -> 1.6.28-1+deb9u1 [UPGRADE] libpq5:amd64 9.6.11-0+deb9u1 -> 9.6.12-0+deb9u1 [UPGRADE] linux-image-amd64:amd64 4.9+80+deb9u6 -> 4.9+80+deb9u7 [UPGRADE] python3-cryptography:amd64 1.7.1-3 -> 1.7.1-3+deb9u1 [UPGRADE] rsync:amd64 3.1.2-1+deb9u1 -> 3.1.2-1+deb9u2