Adding links to a m:n relationship from as BPM

[esendino]

Hello.

I'm using version 8.4.

I need to add a many-to-many link and I'm having trouble adding it from a bpm

The tables to be related are:
TSMovimiento
FCHecho
Neither of these entities has a formula to be executed before saving, nor any API requests for formulas, nor any Hook.

And this is the relationship definition:
Entity: TS Movimiento
Link: tSMovimientos
Type: many-to-many
Foreign Link: fCHechos
Foreign Entity: FCHecho

I have a BPM with TSMovimiento as the target entity. There's a script task with this code:

$prFCHechoAddId = '69629f1f76bd448aa'; //example to be added. Yes, it exists
$prFCHechosAddIds = list($prFCHechoAddId);

// To get the data before the relationship
$prTSMovObjetoAnte = record\fetch('TSMovimiento', $prTSMovimientoId); // $prTSMovimientoId is the current record

$prRelacion = record\relate('TSMovimiento',
$prTSMovimientoId,
'fCHechos',
$prFCHechoAddId);

// To get the data after
$prTSMovObjetoPost = record\fetch('TSMovimiento', $prTSMovimientoId);

Execution Results

$prRelacion: true. This means it worked correctly.

In $prTSMovObjetoAnte we see "fCHechosIds": [ "6953899170b9d0ad2"] // The process starts with just one FCHecho related
and in
$prTSMovObjetoPos we see "fCHechosIds": [ "69629f1f76bd448aa", "6953899170b9d0ad2"] // The process ends with two FCHecho related

That is, the link was added correctly.

However, when, after that, I see the TSMovimiento the added link has disappeared, only remains the original one.

And if I run it again, it repeats the same cycle. It adds the link and then it disappears

As I mentioned, there are no hooks nor Formula for these entities.

Any ideas what might be happening? How can I trace what is happening?