What it sounds like to me is that you have not checked the box “Automatically apply new threshold changes” at the bottom of the Zones settings page, so you are receiving suggestions to make a change but they are not actually being applied. Otherwise it doesn’t make sense for the system to move your pace up and down like that over such a short period of time. If you do have that setting checked, maybe get in touch with TP support? They are very responsive.
Someone correct me if I’m wrong, but I don’t think threshold HR and threshold pace have any connection in TP. If you maintain a new high average pace for 45 min, you will always receive a threshold change notification/suggestions, and when you maintain a new high average HR for 45 min, you will also receive a change notification, but the two have no affect on each other.