[Miscellaneous Android Development] psychofad:
Sounds like a driver issue, best way (for me at least) to get the Preloader Vcom Driver loaded properly is to shut the phone all the way off, open Device Manager on your pc and watch the serial ports section, hold both vol+ and vol- at the same time while reconnecting the usb to the phone, the usb device that shows up when you do is the one you want to get a driver on, he's a quick one, because he will go away (windows device disconnect sound) and then his brother shows up to fake you out. It a fun little whack a mole game to begin with but there is a way to deal with this, if you click the view menu on device manager, then show hidden devices, you will see him all greyed out, to be sure its the right one you right click him, choose properties, click the details tab, change the properties selection to "Hardware Ids", and look for the one that has a value of "usb\vid_0e8d&pid_2000" (note the pid_2000). Now, to win this game of whack a mole, go ahead and click the driver tab, click update driver, browse my computer, let me pick..., have disk, and basically do all but the last step on changing the driver then....plug in you usb while holding the volume buttons again and when he turns solid, click the ok to change the driver! If you timed it right you now have the preloader driver loaded onto the right com port, and the next time you use SP Flash you just click the readback button, hold both vol buttons and connect the usb cable and it should complete easy peasy!

For full readback on my device I found that I needed also to have the usb device with the Hardware Id of "USB\VID_0E8D&PID_0003" (pid_0003) to have the "MediaTek USB Port" driver loaded. This driver is part of the vcom driver package (same one just a different function really) you just may have to go through the steps of updating the driver and once you get to the point of clicking Have Disk, instead uncheck the box that says show only compatible devices and pick the MediaTek USB Port one from the list that appears.

This is a pain I know, but you only have to do this crap long enough to get your drivers set up and then you can forget about it until the next time you reinstall windows lol!

Good Luck!:eek::laugh:

---------- Post added at 12:41 AM ---------- Previous post was at 12:22 AM ----------

Well, until I figure out how to fool LK (little kernal, the other part of the preloader in our phones http://www.lieberbiber.de/2015/07/05/mediatek-details-little-kernel/) I won't be flashing any recovery. He replaces recovery every reboot (those disconnect, reconnect sounds) to make sure system is secure. MediaTek, such a fun journey! If we can bypass or turn off this functionality we should be able to "fastboot boot recovery.img" without this happening, then I will flash it, no sense taking unnecessary risks ya know! Since you have rooted already, try renaming the file "recovery-from-boot.p" in your system partition, I know this is used to replace the recovery on reboot but I am unsure if this is LK's method yet, got to go grab Magisk and root my boot.img so I can start digging around trying things. Historically, renaming and/or deleting this file has been the method of dealing with it's effects from what I read so far without any ill affect, I would think renaming is the best option as it provides the easiest way to return to stock before the Pie update next year. :D