I had similar issues with an RX5700 too. Tried everything that SE and AMD suggested and still had issues (in end turned out to be faulty chip on board but couldn't get replacement so exchanged for a Nvidia card in the end). Aside from what Barristan has suggested you could also try the following:
1. Ensure that the card is not overclocked in any way. I think there is some suggestions to underclock it slightly (you'd have to Google this as don't have refs to hand).
2. Adjust display rate - especially if using Freesync (turn Freesync off!) - I dropped it down to 60Hz and this did seem to help (not completely stop the problems but helped reduce the number of crashes).
3. Ensure your Antivirus is not set to actively scan your driver or FFXIV folders (some cause issues with the directx files from what I've seen).
4. Ensure the AMD overlay is not enabled.
Hope you get it sorted soon![]()