Frequent, in older biblical English, can mean abundant, more numerous, widely spread, or occurring in greater measure. It does not necessarily mean repeated often in the modern sense. The related idea is abundance or broad distribution.
The King James Version uses “more frequent” for Paul’s abundant sufferings in prison, while the Revised Version reads “more abundantly.” In a marginal rendering concerning visions, frequent means widely spread or made broadly known.
The English word comes from a Latin term meaning crowded. The supplied material notes that later translations commonly use abundant, profuse, or widely spread instead of frequent in these passages.