Use 4 lithium batteries in series, old laptop battery, or a 12V 7 Ah battery, rather than faff around with buck boosters.
They will last a lot more time also compared to the duration of play from the power bank you are using.
And those power banks themselves have a 3.7V battery inside, with a boost circuit to give 5V.
Effectively, you have two boosters in series, and that is like sticking your finger in a moving bit of machinery, or shooting yourself in the foot.
Too much interference from switchers in there, and two are going to all sorts of problems when in series.
They will last a lot more time also compared to the duration of play from the power bank you are using.
And those power banks themselves have a 3.7V battery inside, with a boost circuit to give 5V.
Effectively, you have two boosters in series, and that is like sticking your finger in a moving bit of machinery, or shooting yourself in the foot.
Too much interference from switchers in there, and two are going to all sorts of problems when in series.