After upgrading from 10.3.29 to 10.3.30 we started hitting "Update locks cannot be acquired during a READ UNCOMMITTED transaction" errors which did not occur in previous versions.

Recreate test case DB with the attached test-case.sql and perform this query:

SELECT * FROM polygonassets p WHERE ST_Contains(p.shape, (SELECT point FROM pointassets WHERE id = 0x000007158cce4a99950bb6589b31ab1b));

This will result in:

ERROR 1207 (25000): Update locks cannot be acquired during a READ UNCOMMITTED transaction

Might be related to MDEV-26123?