I am working with corrplot library and this is the code:
corrplot(correlation_matrix, method = "number",
number.cex = 0.6,
tl.col = "black",
type = "lower",
tl.srt = 45)
Surprisingly it outputs this strange plot:

Any idea why this happens? I build the correlation matrix directly looking from the documentation.
I found out how to fix it. I have to specify "corrplot::" as follows:
And the result is: