Problem with left-join

Hi guys I have a problem with KStreams. I have a KTable T1 on which I perform a left join on a KTable T2.
The result is converted to a KStream.

I would like for each update in table T2 the left-join to publish a message. But this does not always happen.

Sometimes I am forced to do a dummy update of T1, then later I can update T2 as much as I want and get the behavior I want.

Is it basically wrong to expect a join update when only the aggregate table is changed?

I also attach a piece of code to make the problem clearer.
ProductFacility is the table I would like to update.

    kStream = productKTable.getKTable()
                    (product, productFacilities) -> {
                        if(productFacilities != null){
                            var facilities = new HashMap<String, ErpProductFacility>();
                            for (var productFacility : productFacilities) {
                                facilities.put(productFacility.facility, productFacility);
                            product.facilities = facilities;
                        return product;

Any help will be appreciated. Thanks in advance.

KTable by default use internal caches. You might want to disable caching, either globally for all KTables setting cache size to zero in the config, or on a per-table basis (for both input tables) by passing in a Materialized config object.

Cf. Kafka Streams Memory Management | Confluent Documentation