Verb agreement for something that was discussed in the past, while the issue still exists in the present [duplicate]
If you want to express that the problem still exists, you should refer to it in the present tense. Note that it is quite possible to use words to describe the DISCUSSION in the past tense, but the PROBLEM in the present tense. For example, "Yesterday we discussed [past] a problem that is troubling [present] our nation."
All are possible, and the difference is one of focus rather than objective fact. The first variants (1; 1') imply that the issue still exists in the present; the second do not imply that, but neither do they imply that the issue no longer exists.