I have a long data frame of authors with their scholar ids. Running get_publications sequentially on this list produces random 404 warnings, and NA is returned. For example:

get_publications("ri2FkCgAAAAJ")
[1] NA
Warning message:
In get_scholar_resp(url) :
Page 404. Please check whether the provided URL is correct.

It is strange that this error is random. For example, if i have a table with about 1000 authors, the first error may appear for the author in line 150, and all previous authors are processed without problems. After some time, i may run the code again and the problem may appear for some other author.
I also tried introducing random wait times between each search, but the problem persists.
Any ideas?

What i basically want to do is derive the number of publications of these authors in a certain time period (in years) and the number of cites to these publications.