After the 1990s ME had become CFS which had a much wider definition. It was also so unspecific that it was possible to cherry pick patients so the negative results found by the psychologists at the Nijmegen Group in the Netherlands is not surprising.
The whole sociology, if that is the right term, of enteroviruses is fascinating. There is this whole myth that only polio was dangerous and that has been conquered so the rest are common and mild infections so not worth bothering about.
But serious enteroviral disease still exists. Acute Flaccid Myelitis (called acute flaccid paralysis in the US) still comes in epidemics and is very similar to polio, yet the CDC denied it was enteroviral for a long time, claiming that everyone has antibodies to enterovirus.
I was at a talk by John Gow and he did not seem to realise that polio was a simple respiratory disease in most people who got it, with only a few developing classic polio. If ME is caused by an enterovirus then it is only a few people who get infected who go on to get ME.
Enteroviruses are still difficult and labour intensive to detect. PCR only looks for enteroviral RNA but that is like looking for the presence of coronavirus without checking for SARS-CoV-2. It is useful for acute infection but not for ME studies.
Though they are wonderful viruses with all sorts of tricks to avoid the immune system. Since viruses only use energy for what is useful, dropping things that are no longer necessary to them, it is hard to see why they have these abilities unless it is to let them persist after acute infection.
The evidence indicates that enteroviral ME exists and accounts for many patients.