I don't understand the Avherald story. As I understood it they declare an engine failure then as they got it back they said we have two good engines several times.
I never heard anything about dual engine problems and it was pretty clear it was "two good engines" rather than "Two red engines"
Listen carefully...... First they had two "red" engines, after a while they solved the problem (you can hear the other guy in the background) so here's a clue what might have been going on.....
------ My opinion -----
They took of from rwy 11 which isn't too long, the 757 has EPR which can be manually controlled by setting the temperature so the engines are able to run hotter than normal...
Sometimes this EPR runs out of sinc and both engines get too hot (that is: the EGT gets too hot and need first 5 minutes to cool down, then 10 ect.)
There are 6 push buttons on a 757, TO/GA CRZ, CONT, CLB and two manual EPR knobs...
It is somesort of rule of thumb to push either button first before take-off, cause of the runaway EPR...
It is also solved by pushing crz or to/ga again and engnes will operate normally...
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This will only be if there wasn't a birdstrike nor nosegear blown.... So we have to wait for the official statement, but my guess it the above.....