Sorry, I know, it was a typo, I meant to boot to it using fastboot.
I also had Spes, months ago, and I never had the kind of issues you are facing. Although that said, there is some specific builds that don´t allow TWRP to be flashed, why? because they integrate the recovery into the ramdisk partition, if you replace that recovery (maybe CrDroid), device won´t boot.
Also you can try by booting to fastbootd, using adb reboot fastboot
, or from fastboot (bootloader mode) with fastboot boot fastboot
, in the userspace is possible to target directly to the ramdisk, not sure if it works with spes, using fastboot flash recovery_ramdisk twrp.img