In your lanelet map OSM file, the <node> coordinates are available in 2 different forms: latitude/longitude and MGRS. For example:

<node id="30" lat="13.801094196677974" lon="100.54001559798192">
    <tag k="mgrs_code" v="47PPR664262"/>
    <tag k="local_x" v="66467.4103"/>
    <tag k="local_y" v="26262.2704"/>
    <tag k="ele" v="-27.514"/>
  </node>

You say your map overlaps over 2 MGRS zones, which is likely the cause of issue. For example, Autoware may not check the mgrs_code or local_x/local_y files under some conditions, while the lanelet map editor will correctly parse them (see https://autowarefoundation.github.io/autoware.universe/main/map/autoware_map_projection_loader/).

For example if you have set the map projector to MGRS in the map_projector_info.yaml file, then the local x/y coordinates are ignored and only each lat and lon values are used. This projector assumes all points are in the same MGRS zone. If that is not the case, you should see the following warning:

https://github.com/autowarefoundation/autoware_lanelet2_extension/blob/c148815f4483a9acd51bd25abcb26a7a5a99381d/autoware_lanelet2_extension/lib/mgrs_projector.cpp#L63-L68

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I encountered the same problem. Could you please help me with how you solved it? Thank you!

The error "some points have negative xy-coordinates in MGRS coordinate system" that appears when using the vector map builder software essentially arises because MGRS should have the bottom-left corner of the zone as the origin, but in this software, the origin is set to the vehicle center. This causes a shift in the origin of the constructed map, leading to negative coordinates.

To resolve this origin issue, the origin should be moved to the bottom-left corner of the MGRS zone.