A common mistake video creators make is in distinguishing between the different types of copyright involved in music. This includes classical compositions which are obviously in the Public Domain due to age. Any piece of music has at least two, and possibly as many as four copyrights involved.
The first is of course, for the composition itself. The second would come into play if there are lyrics involved in the musical piece. I know of at least two modern recording artists who based songs on Public Domain classical compositions and now have copyrighted recordings based on these pieces with lyrics added. The sound recordings themselves are the third copyright type; and this is most likely the source of
@sydh's problem. The fourth copyright would be for the arrangement of the music.
You see, a composer can be dead for a century or more; but the minute a new arrangement of the music is done, that arrangement comes under copyright. Any recorded performance of the music would also be under copyright, unless the recording is also more than 100 years old. 100 years after production is a safe point to consider something to be out of copyright in general; as when the Digital Millenium Copyright Act was written, and countries cloned it for their own use, it was stated in different ways, according to the country applying it.
In the USA, where this law originated, copyright is in effect until 75 years after a recording artist's death, unless it is renewed by the record company which held the recording contract. Same for composers, lyricists and arrangers, unless a legal heir somehow exists and wants to renew the copyright.
I know
@sydh will say this doesn't answer his question, so I will give an answer to footnote this explanation.
No; you can't avoid constant copyright claims if you use recorded music which may still be under copyright. As different orchestra recordings of a work may sound similar, Content ID's algorithm finds false positives all the time. The only way to avoid claims entirely, and even this doesn't always work (I am living proof of this), is to compose your own music for use in your videos.