(I confess; That was my whole question, but StackExchange won't let me post this until I 'meet their quality standards' by writing something about 'my problem' in this body-text.')
No. The three synoptics, Matthew, Mark and Luke have never been disputed in their united descriptions of Jesus. There was an issue about the authenticity of John...
The issue centred on when John was written. Basically was the author John an eye-witness to the events, as that gospel states, viz. John 21:24–25,
"This is the disciple who is testifying to these things and has written them, and we know that his testimony is true...",
or was it written so long after the event the above statement was fabricated?
The prevailing view within linguistical dating of John historically was that is was written so far after the event John couldn't have been the eye-witness. I do analytics and in temporal analytics it's very easy to get it badly wrong (except for my stuff of course).
Crazy late dates emerged for the origins of John following linguistic reasoning that were long after the life of John, at 200AD. Unfortunately for these linguists the Rylands Library Papyrus emerged in Manchester, UK. This papyrus is a fragment of John's gospel that was dated by carbon-14 (C14) to be around 125AD, it could be earlier however (90AD). OOoops because the proposed dates were notably later than the earliest known existence of John's gospel in modern times. They'd got it wrong and must have felt silly. 90 AD is a possible date for John and within the lifetime of John, but given the track record of guess-work here and the C14 dating ... if Rylands papyrus is from 90AD then John's gospel was originally written even earlier, i.e the papyrus is a copy of the original.
In analytics get something badly wrong it means no credibility and no-one believes you anymore *
Summary, there is no convincing evidence against the authenticity of the gospels and the one gospel subject to dispute, John, states they were an eye-witness and is supported by C14 studies. It's very strong evidence. Thus there is no object evidence to dispute that the 4 testaments of one man is anybody else but Jesus.
*, If I was a theologian I'd use modern advanced statistical analytics to re-date the entire origins of John feeding in the Rylands Library Papyrus into the model. It's highly amenable to my specialism, known as phylogeny. From my professional perspective I'd wipe the slate clean, start over.
The Authorised Version contains "The Gospel According to St. Matthew", "The Gospel According to St. Mark", "The Gospel According to St. Luke" and "The Gospel According to St. John". Those four accounts of the birth, life, death and resurrection of Jesus of Nazareth are clearly accounts of the one man.
However, there likely will have been individuals throughout the centuries who thought those writings were about more than this one man, Jesus of Nazareth. Who they were is not known to me. They would have had to write down their case for that idea, or to have set up their own religion based on that idea. What is certainly known is that after Jesus of Nazareth died and then was resurrected, his warning about "other Christs" arising, purporting to be him, started to happen. There have been many pseudo-Christs, from the first century till this day.
Here is an example of such a warning, from the lips of Jesus himself, before he died:
"Then if any man shall; say unto you, Lo, here is Christ, or there; believe it not. For there shall arise false Christs, and false prophets, and shall shew great signs and wonders; insomuch that, if it were possible, they shall deceive the very elect. Behold, I have told you before." Matthew 24:23-25 A.V.
This is also recorded in Luke's gospel, in chapter 17 verse 23, and in Mark's gospel, in chapter 13 verse 21. John identifies this Jesus as do all the others, in John chapter 1 verse 40, as the promised Christ, the Messiah. None of the four writers even make any ambiguous statements about Jesus, that might give rise to the idea that they were actually writing about two different people. Reading all four accounts consecutively would dispel the idea that they could have been writing about more than one Jesus.
However, in the first century, some religious people who were not Christians tried to get Christians to believe that Jesus was either not a real human, or that he was not really the incarnation of the Son of God. The rest of the New Testament has several places where this gnostic-type thinking was warned against. In a sense, such false teaching was about "another Jesus", a Jesus different to the one the gospel writers wrote about. But it required belief in either one, or the other - both could not be believed in simultaneously. So, that does not meet the criteria of your question. This leaves the simple answer to be, "No, the four gospel writers were all describing the one person, Jesus of Nazareth, who they believed to be the Son of God, as proven by his resurrection from the dead."