Custom insert by @Query() on R2dbcRepository method fails silently without an exception ? How can i make this work?

Question

I'm using 'org.springframework.boot:spring-boot-starter-data-r2dbc' and 'org.springframework.boot:spring-boot-starter-webflux'. 3 different datasources (works, following spring.io docs, fine) using a spring repository (R2dbcRepository) to save/insert/update/query 3 different entities into 3 different tables "users" "roles" and "user_roles" (basically trying to convert a blocking api to a non-blocking one). To insert new rows into "user_roles" i configured a custom query

@Transactional
@Modifying
@Query(value="insert into user_roles(userid, roleid) values('?1', '?2')")
Mono<Long> saveRoleidAndUserid(Long userid, List<Long> roleids);

which silently fails (no new rows are inserted without an exception).

inserting with entityTemplate

userEntityTemplate
            .getDatabaseClient()
            .sql("insert into user_roles(userid, roleid) values('"+userroles.getUserid()+"','"+userroles.getRoleid()+"')")
            .fetch()
            .rowsUpdated()
            .subscribe(x -> logger.info("rows inserted: "+ x.longValue()));

or from postgres (with the same query) works fine. Also inserting with the same userRepo.save(User user) for "user" objects works fine too. The role table gets initialzed once (with a couple of roles to query) and also inserting with save () works fine, too. How can i get the custom insert to work with @Query() annotation ? Thanks in Advance.