Without even getting into ancient or medieval times, there is certainly evidence of anti-semitic attitudes in a number of popes over the past 200 years. Probably more in the 19th century than the 20th. Of course, Catholics will deny this.
I suspect that is is because RC's do not understand the atonement and they blame the Jews for hanging Jesus . I have heard RC's discuss it Jesus had been "allowed " to live..
Jhn 10:17 Therefore doth my Father love me, because I lay down my life, that I might take it again.
Jhn 10:18 No man taketh it from me, but I lay it down of myself. I have power to lay it down, and I have power to take it again. This commandment have I received of my Father.
This was always Gods plan...