I saw the 2 reports, and have also the same problem. version 1.0.0.56 (241523)
I am Rome, and for ages now (200 turns?), I have an Open Border and Alliance with Cleopatra. I never went at war with her, and had excellent relationships with her since I discovered her civilization (turn 20 or so... I am turn 326 now)
Around 150 turns before, still in open border+alliance, I received a message (the grey banners with news) saying "Our agent reports that Egypt is launching a massive attack on Rome". I saw numerous egyptian units around my capital, and they start taking my civilians...
Since then, their units always attack me, and kill my own units, in her territory (ex, scout passing by), in neutral territory (ex.: high sea), and inside my borders...
I can even attack and destroy her units, bombard her cities, etc, in and out any border, and all that without a single penalty from her side (her relationship points are always the same...).
(trying to upload a saved game, but always receive the message (Addblock disabled):
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TRAJAN 326 1525 AD-egypt vs rome.Civ6Save)