Import data from excel but get warning messages

I import data from excel and I have multiple excel so I read at one time.
Here is my code:

library(readxl)
library(data.table)
file.list <- dir(path = "path/", pattern='\\.xlsx', full.names = T)
df.list <- lapply(file.list, read_excel)
data <- rbindlist(df.list)  

However, I get this warning messages between df.list <- lapply(file.list, read_excel) and data <- rbindlist(df.list).

Warning messages:
1: In read_xlsx_(path, sheet, col_names = col_names, col_types = col_types,  :
[3083, 9]: expecting date: got '2015/07/19'
2: In read_xlsx_(path, sheet, col_names = col_names, col_types = col_types,  :
[3084, 9]: expecting date: got '2015/07/20'

What's going on? How can I check and correct?

According to my comment I submit this as an answer. Have you looked into your excel sheet at the respective lines? to me it seems that there is something going on there. maybe you have an empty cell before or after these lines, some space or anything like that... or the format of your date is different in these ones from what is in the other cells.