PRAM reset twice, boot menu doesn't show external boots

[alfon_sico]

Recently I change my Mac mini 2012 with a 2014

I work for some days with HDD inside and SSD plugged in USB 3 with no problem switching with them

Three days ago I switch physically HDD an SSD and everything works right but yesterday take aware that when I enter in ALT boot menu it doesn't show nothing but internal SSD and SD with macOS installer

I reset PRAM and apparently works the first time that I boot

Today happen me again, ALT boot menu doesn't show external devices with macOS. It show internal one and USB/SD with "installations"

Again Reset PRAM and again it shows well my Mojave external drive plugged in the same USB3

 

[alfon_sico]

I delete every file in EFI partition of every drive I use but still get a erratic behaviour

If I reset PRAM I always get shown every drive connected in boot menu
Then I can't say exactly why there is sometimes that get recognize and others don't (changing the USB plug, turn off and on doesn't get nothing).

If I boot with principal drive I revise "boot drives" setup I can choose the others but they doesn't show every time in boot menu