As far as I know, there have been aspects of society that have continuously claimed that our society is degenerate and that the past used to be better, only to have similar claims be made in the past. Was this fear of societal moral decay as prevalent during the Middle Ages as it was during the last two centuries or so?
In many ways your question is related to one asked on how historians can study the past and not become nihilists: https://www.reddit.com/r/AskHistorians/comments/kza2g9/this_is_a_bit_of_a_different_question_as_a/
So you may find some insight there. The problem with answering it is that you are making an assumption which I think is probably false. Your assumption is that some people in some places thought current society was a degeneration from a superior past. In fact it would probably be more accurate to say that almost everyone in almost all places where a historical literature developed has thought like this. The Greek writer Hesiod describes a scheme in which the current state of the world is a decline from a golden age. In India, and this is very much picked up in the medieval period, there is the notion of the Kali age, that our current time represents a final degradation from a superior past, which first appears in writing in the fourth century AD. Buddhist literature is replete with properties of how degraded society will have become 500 years after the death of the Buddha (these tend to be written as prophecies). It is a common trope in Islamic and Christian historical writing that current events are particularly awful as a punishment for a lack of piety.
Today our historical understanding is based much more on evidence rather than sentiment and so we know it is not true, we know that in very broad terms things have broadly gotten better in human society and continue to do so (for the arguments on this you could look at popular books by Ian Morris such as Why the West Rules, and The Measure of Civilization). Yet human being still seem generally inclined to believe things are getting worse, that civilization is teetering on the brink of final collapse. I cannot give examples due to the rules on referencing recent material but you will have read a newspaper headline.
The real question is not whether some medieval people thought that way, yes they would have because most people have most of the time, but rather explaining the exceptions - why did people seem so positive at some specific moments, under the Roman Emperor Augustus, the Whig historians, or in the late 1960s.