Invalid UTF-8 string (problem with umlauts in callerid)

Hello,
we are currently experience some problems with our asterisk installation. Every time there are umlauts (we are located in a german speaking country) in the CallerID we receive the following error messages:

ERROR[19407][C-0000006c] json.c: Error building JSON from '{s: s, s: s}': Invalid UTF-8 string.
ERROR[19407][C-0000006c] : Got 12 backtrace records
# 0: /usr/sbin/asterisk(ast_json_pack+0x94) [0x4f7ca4]
# 1: /usr/sbin/asterisk(ast_channel_publish_varset+0x2b) [0x57e2eb]
# 2: /usr/sbin/asterisk(pbx_builtin_setvar_helper+0x123) [0x5343c3]
# 3: /usr/lib64/asterisk/modules/app_mysql.so(+0x2e9f) [0x7f77aff5de9f]
# 4: /usr/lib64/asterisk/modules/app_mysql.so(+0x378b) [0x7f77aff5e78b]
# 5: /usr/sbin/asterisk(pbx_exec+0xb9) [0x52b1b9]
# 6: /usr/sbin/asterisk() [0x51eb85]
# 7: /usr/sbin/asterisk() [0x520bf4]
# 8: /usr/sbin/asterisk() [0x52217b]
# 9: /usr/sbin/asterisk() [0x59e7a9]
#10: /lib64/libpthread.so.0(+0x7dd5) [0x7f781b3d2dd5]
#11: /lib64/libc.so.6(clone+0x6d) [0x7f781a77502d]

os -> centos 7
asterisk version -> 16.5.0
jansson.x86_64 -> 2.10-1.el7
jansson-devel.x86_64 -> 2.10-1.el7

I am not quite sure why this problem occurs. We used an older asterisk version before and never had any problems with umlauts on that installation.

Thank you for your help!

EDIT: added formatting

I had the same problem. Asterisk does not like accent characters.