@Sjoerd Bakker I think it is never pointless to ask a question here as most of the times, the most reliable information is coming from fellow travelers. And even if it would be too late for me, maybe it would be useful for others. So still excellent to confirm a situation. As for the spelling mistake, thank you for pointing that out. It was an honest miss-type due to writing in a rush at one of the many tourists traps in Palenque. No disrespect intended for the actual place! And your advice for the roads to take from Palenque onwards and we indeed highly enjoyed and recommend the back roads north of Palenque
I asked last night because just then I discovered this thread. Before this, people that I've asked about this elusive border crossing had various opinions ranging from it does not exist to it does but the only Banjercito is in Tuxtla Gutierez. So this thread was very helpful for us.
Even with the schedule of the Banjercito it was so fanny: everybody we asked on the road from Tenosique to El Ceibo said that it is open today (Monday). Police guys at the 2 check points, the military guys and the top of the top... the border guys at the border crossing itself. We stopped, we asked if the Banjerito is open and they said yes and motion us to park the bike so they could check it!!
We were starting to reach for our documents when another guy came from the Adauna building and said to our first guy "Hey, man, today is Monday, they cannot pass today as the banck is closed". This alone made the trip to the border worth it (and it was a ride with nice views too).
So heads up for other travelers: The Banjercito is indeed still closed on Monday!