Zabbix server does not have enough buffer size for reading DB.
Because in spite of reading as UTF-8, it fixes the words length, e.g FUNCTION_PARAMETER_LEN is 255 and FUNCTION_PARAMETER_LEN_MAX is 256 for varchar(255).
Though almost are correct because UTF-8 characters are block in inputin time on WEB UI, especially 'parameter' of functions tables is accept for UTF-8. So, its buffer size must be (FUNCTION_PARAMETER_LEN * 4 + 1).
I attached the patches for 1.8.19 and 2.0.10. There is a same problem in 2.2.x. But I do not use yet.