Hello,
If you have performed firmware update with Keep settings option enabled, there is a likelihood that some functionalities might not have migrated properly, since there is a big difference between the firmware versions that you have mentioned.
The first thing, I would like you to try, is to reset the router to factory default settings, using one of the methods described here.
Next, check instructions to configuring Bridge/Passthrough modes from this link.
If the issue still persists, I would like you to attach a troubleshoot file to your question. Please, replicate the issue, then access router's WebUI, go to System -> Administration -> Troubleshoot section and download troubleshoot file from there.
Best regards,