Issue only occurs with both ATT and TipTac loaded. If one is disabled there is no issue.

No Lua errors are reported.

I have tried with all addons disabled except these 2 and the issue still occurs.

No reports of this in the past two years, going to assume resolved.

Interesting, I've only noticed this at a very small scale (like a period being moved back and forth) as I've always used TipTac while working on ATT. It seemed to only happen to specific tooltips (like Garrison Shipyard rewards...) and was due to the text wrapping within the tooltip. I feel that this would require some research into how TipTac modifies tooltips to determine the root cause and develop a fix, either from ATT's end or TipTac's.

In your particular example, it seems the only ATT-related text which is on the tooltip is the 'Specialization Icon' at the bottom. Curious if turning that setting OFF in ATT would still cause this issue? (Settings > Tooltips > Show Specialization)

Just checked now and turning off specialization stops the flickering for things like xmog and conduits. But for world quests that reward pet charms it still occurs as ATT is displaying all of the pets I can buy.

An odd thing I noticed is that holding down SHIFT stops the flickering regardless of whether tooltip integration with modifier is enabled in the ATT settings. So that might indicate that the problem lies elsewhere.