John
I had a look at the Le Strange side. It does indeed look like you might be on to something.
First, it is interesting that from the beginning there were always two Le Strange families in Norfolk, obviously likely to be closely related. The main one, later also marcher lords, is associated with Hunstanton but there was another family specifically in Litcham. A convenient summary can be found in Carthew's Launditch Vol. 1:
http://hdl.handle.net/2027/yale.39002040741580?urlappend=%3Bseq=168
By the way here is his Felton tree (note the footnote c):
http://hdl.handle.net/2027/yale.39002040741580?urlappend=%3Bseq=178
I am not saying this is the family involved, but I mention it as a starting point because I suppose there will have been generations where there were Lestranges of both lines with similar names.
Another branch which may well be relevant is the one in Walton d'Eiville and the manor spelled sometimes as "Middle". This was covered in a short note of 1946, by Cecil L'Estrange Ewen. I think it can only be found online behind paywalls. I suppose you will know this is a subject of a CP correction here:
http://www.medievalgenealogy.org.uk/cp/strangeofknokyn.shtml
This branch descended from the same John Lestrange (V of Knockin) we are discussing, but through a second wife Maud. Confusingly, he had two sons named John, one from each wife. Maud was the heiress of Walton d'Eiville and her son John is that start of that line, whereas Elianor de Montz' son John became John IV in the main Knockin line.
One obvious thing to check is the birth year estimations of John Lestrange V of Knockin. A convenient collection of information is here, in Hamon LeStrange's book about the family:
https://archive.org/stream/lestrangerecords00lond#page/184/mode/2up
(It is old enough that it still struggles with the identity of his two wives, but that is not relevant here.)
It says he was 22 when his father drowned in the Severn in 1275. That sounds like his estimated birth year of 1253 is a fact people have checked, and could check, so I will leave that there. It means he will not have conceived legitimate children normally before say 1270, but more likely after 1275 and his father's death.
Cecil L'Estrange Ewen's article clarifies the wives, and shows also roughly when the marriage must have occurred. Again the CP summary seems correct concerning that. So there seems no problem with John's birth and marriage dates. Indeed the CP correction cited above indicates that Eleanor probably had her children in the 1280s.
We have to ask what evidence ever led to Felton being specifically married to a daughter of John V of Knockin and Eleanor. It does not seem clear.
Hamon LeStrange does not place this Felton marriage in the Knockin tree, as will be seen at that page, but he does mention Robert Felton in several places, including once on a page facing his version of the Litcham tree:
https://archive.org/stream/lestrangerecords00lond#page/52/mode/2up
He also mentions Felton in connection with legal cases also associated with Thomas Hastang, who Hamon LeStrange (and Eyton) could not explain well. For example:
https://archive.org/stream/lestrangerecords00lond#page/268/mode/2up
https://archive.org/stream/lestrangerecords00lond#page/308/mode/2up
The later article by L'Estrange Ewen clarifies who Thomas Hastang was: he remarried to Maud the heiress of Walton d'Eiville after the death of John V of Knockin. Therefore John Lestrange of Muddle, the king's yeoman mentioned in some of these references, is John Lestrange of Walton, the son and heir of Maud.
I have already cited Carthew above who raised more or less exactly your question. "Lord Arthur Hervey does not give his authority for inserting the name of John le Strange as the father of Matilda."
Here is a suggestion Carthew makes about a possible line of investigation:-
"There was a possible derivation of the Feltons from Le Strange to be found in Mr. Eyton's work which may be mentioned here.
"One of the Le Stranges named Hugh, with his brother John, were witnesses to a charter of Guy le Strange in 1174.
"Hugh was dead in 1240, and his inheritance in Shropshire divided amongst females, being held under John le Strange of the Fitz Alan fief.
"In 1255 the persons representing these females, but whether sons or husbands of four cohieresses of Hugh le Strange is not known, were —
"1. Richard de Drayton ;
"2. William Fitz Alan, or son of Alan de Drayton ;
"3. John Fitz Phillip ;
"4. Philip de Hungefort.
"Richard de Drayton was dead before 1292, and Thomas de Felton was his heir.
"Stephen, son and heir of Thomas de Felton and Sibil his wife, was born in 1281.
"But neither these Draytons or Feltons seem to belong to Norfolk."
But I don't find this lead very promising?
Best Regards
Andrew