According to Benoît Peeters' biography of Herge, a clairvoyant named Bertje Jagueneau was the origin of a quarell between the two men
I find this rather odd myself. Mind you, some sources, including Michael Farr, suggest that Hergé took this sort of thing quite seriously: he believed in dowsing (Calculus and his pendulum) and he and his second wife were also interested in telepathy (Tintin's dream of Chang in "Tibet").
I'm wondering if he seriously believed in the possibility of aliens - aliens who did not want to be seen. That would explain why he stuck to the rather ludicrous outcome of "Flight 714".
One should also consider the fact that even many highly-educated people like politicians are rumoured to consult astrologers and such like; Cherie Blair, a top barrister and wife to the Prime Minister, for example. The Nazis are said to have done it as well. Granted, they were mad, but all the same...
seemingly prevented him getting the editorship of Le Journal Tintin
Actually many sources indicate that he was the editor at some stage, at the very least during the early years of the magazine. Farr mentions him as such on page 138 of "Tintin: The Complete Companion".
There is a French biography of him called "A l'Ombre de la Ligne Claire - Jacques Van Melkebeke, le clandestin de la BD" ("In the Shadow of Ligne Claire - Jacques Van Melkebeke, Comics Underground").A review of this book
claims that he actually did edit "Tintin magazine" anonymously, contributed as a script writer under various pseudonyms and was very much involved in the post-war developments of "Tintin" and "Blake and Mortimer" - though a reader's review notes how his daughter won't talk about this aspect of her father's work.
It's available on Amazon.co.uk for French readers
Mind you, most of the sources seem to focus on the immediate post-war period. I can't seem to find anything about his work during the late 1950s, 60s etc.