"Duplicate entry"-error without duplicate. utf8-problem?

[NuFa]

Hi,

I´m trying to transfer a ms access 2016 database to mysql. Most of the records are working fine, but at one table I get "Error: -2147217900" at a few records. Every time there are two "similar written" values, one with an one without special character. A sample:

id; optionID; value; position; media_id
69; 6; metal; 0;
70; 6; métal; 0;

"id" is the indexed primary key, value was indexed with duplicates, for troubleshooting I disabled indexed without effect. The error occurs everytime there are "special characters" in otherwise same values, like "metal" and "métal". The primary key is no duplicate.

The full error message is:
------------
Table: tbl_s_filter_values
- Table 'tbl_s_filter_values' created
Error moving data
Error: -2147217900
Reason: [MySQL][ODBC 8.0(w) Driver][mysqld-5.5.5-10.5.11-MariaDB-1:10.5.11+maria~focal-log]Duplicate entry '6-métal' for key 'optionID_5'
SQL: INSERT INTO `tbl_s_filter_values` (`id`, `optionID`, `value`, `position`, `media_id`) VALUES (70, 6, 'métal', 0, NULL)
Transfer was aborted