No, this line is perfaectly normal, and it depends on what the values are.
"bpbkar waited xxxx times for empty buffer, delayed xxxx times"
It is the 'delayed' number that is important.
This line is relating to the 'reader' process that fills the bptm memory buffer - depending on the config, it could be bpbkar or bptm.
The bptm log will also contain a similar line ...
... waited xxx times for full buffer, delayed yyy times.
What can be down depends on how high the numbers are, and which of the two times (for a given backup for example) it the highest.
Generally for example.
If the lines show bptm "waited xxx times for full buffer, delayed 890000 times." then changing the buffer size, or increasing the number of buffers 'probably' will have no effect, as the issue is more likely to be related to the speed the data is getting to the media server , due to poor read performance or network.
There is no magic fix that says cahngeing buffer sizes will improved speeds, they might improve speeds, it depends on the reason for the prro performance.
Martin