When I reported  EWHC 466 (Fam) V v M, I suggested that forum non considerations there, moot given that eventually jurisdiction of the English courts was upheld, would resurface in further cases. They have.  EWHC 1995 (Fam) W v L eventually went much the same way as V v M.
The Brussels BIIa Regulation applies when determining the question of jurisdiction regardless of whether there is an alternative jurisdiction in a non-member state (Re A (Jurisdiction: Return of Child)  1 AC 1 , later confirmed in CJEU UD v XB C-393/18 PPU  1 WLR 3083 ). Brussels IIa has an intra-EU forum non conveniens regime (applied in C‑428/15, Child and Family Agency, on which I report here).
Art 8(1) of BIIa provides that the courts of a Member State shall have jurisdiction in matters of parental responsibility over a child who is habitually resident in that Member State at the time the court is seised.
MacDonald J at 30 posits that where the English court does have jurisdiction under Art 8 BIIa but there are proceedings also in a third party non-member state (here: Jordan) the issue becomes one of forum conveniens – which he subsequently discusses following the Spiliada criteria. In V v M to which current judgment refers at 34, Williams J reflected on whether forum non at all has calling following (he held it does; not convincingly). MacDonald J in current case first at 30 simply seems to accept such application. Then at 38 holds he need not decide this issue here (counsel had suggested the issue was in fact covered by Brussels Ia and the precedent value of Owusu therefor clear) for even if forum non conveniens has to be decided, it clearly points to England.
In conclusion, therefore: the issue still has not been settled and will, again, return.