There seems to be some decoding position error. I've not been able to reproduced the issue for now.
Have you the possibility to have a wireshark log for that exchange or enable log level of "org.mariadb.r2dbc" to trace ?

In case logs cannot be enable, query and table(s) DDL would help, because LocalDate decoder is accurate, so i wonder if that can be a wrong position due to previous value wrong decoding

Thanks Deigo. I have attached the trace log (error_trace.txt).

ok, thanks for logs, that has permit to identify the issue.

problem is after reading a MEDIUM value driver leave a resultset pointer in a bad shape : MEDIUM are encoded on 3 bytes server side, but protocol send them in 4 bytes in exchange when using binary protocol.
This remaining byte is actually not read, making other reads on same row completly wrong.

this is corrected with https://github.com/mariadb-corporation/mariadb-connector-r2dbc/commit/08b3e06011c7274fe5a6325e5a15e12cf1f38c0f
correction is available using SNAPSHOT on maven :

<repositories>

    <repository>

        <id>sonatype-nexus-snapshots</id>

        <name>Sonatype Nexus Snapshots</name>

        <url>https://oss.sonatype.org/content/repositories/snapshots</url>

    </repository>

</repositories>

<dependencies>

    <dependency>

        <groupId>org.mariadb</groupId>

        <artifactId>r2dbc-mariadb</artifactId>

        <version>1.1.4-SNAPSHOT</version>

    </dependency>

</dependencies>