The sentence is, for example,
- The researchers investigated and found that due to the rise of AI bots, most of the existing works have focused on protecting the email services from spam.
Is this structure considered wrong speaking of tense use?
The researchers investigated and found that . . .
This part of the sentence happened in the past. The concluding part of the sentence can talk about the past, present or future, relative to that point in time, and still be fine, so long as it is still true:
a) . . . robots had plotted to take over the world.
b) . . . robots are plotting to take over the world.
c) . . . robots will plot to take over the world.
So long as the statement has not been proven to be false in some way since the investigation occurred, the particular time frame is still valid.
For instance, if, many months later, robots are still plotting to take over the word, then b) remains an accurate statement.
This is in line with reported speech where, if the thing reported is still true, you do not need to backshift the tense—it can optionally remain in the present (or future):
Mary told me that she is sorry. (And she still is.)
Mary told me that she will be sorry in 2030. (A date still to come, when, as much as the future can be predicted, something will happen.)
If, however, the thing is no longer a true statement, then the tense should remain in the past—rather than refer to a present or future event or situation:
Mary told me that she was fine. (She has since died.)
Note: To be clear, there are many possible specific verb conjugations that can be used. The actual sentence from the question is perfectly fine.