I'll appreciate it if a native speaker to especially American English would tell me how you feel and write.
This is the only word (that) I know which[that] explains the situation. (A grammar book)
Thus, things you typically encounter that might not usually trigger fear now do so. (This seems to be from a grammar site)
Note that the conjunction (the second that) is usually dropped in this structure; it must be dropped if the relative pronoun is a subject.
This is the woman (who/that) Ann said could show us the church.
(M. Swan, Practical English Usage, 498.15)
After reading M. Swan's, I think (1) should omit the second relative pronoun.
(2) might be correct with the second relative pronoun because the first relative clause is hard to consider as an inserted clause. This is the case of stacking of relative clause, but (1) isn't. (1) is the case with an inserted clause. Am I correct?