I was a bit nervous about trying this bearing in mind my difficulties with previous installations on this device (covered at length here and here) but wrote a new plan and had a go. It worked and I’ll write up the steps here; may be of interest to others having similar problems with this device!
I was going to include one new measure into my plan that I had read about (I forget where) and thought sounded like a good idea: after sideloading the /e/ zip reboot to recovery before attempting rebooting system. It seemed to make the difference but I lack the knowledge to be certain about this.
Before starting, the phone was on the 25 June /e/ dev build on slot B, 30 April build on slot A and had sometime earlier been flashed to Android 8.0 with Androxyde Flash Tool.
Turn on Developer Options and set Allow usb debugging, power off the phone.
Plug into pc in fastboot mode.
Open paltform-tools folder on pc, check test build zip and twrp.img are there, open terminal in this folder.
Enter: fastboot devices , ok, enter: fastboot flash boot twrp.img (I used twrp-3.3.1-6-pioneer.img)(this command is from the Lineage install instructions for temporary recovery)
Terminal shows this step completed, phone still in fastboot mode.Unplug from pc and manually boot into recovery, twrp in this case.
Now follow steps 1.- 8., Installing /e/ from custom recovery in the /e/ documentation and for Step 9 reboot to recovery and unplug device.
Phone will now reboot into Lineage recovery and the following steps are simply what I did and not necessarily the correct procedure. More on this in a minute.
Select reboot: it was unable to to reboot but I left it to continue (thinking bootloop by now!) and it cycled again to the recovery screen with a message something like “…you may need to factory reset”.
Select factory reset: phone boots to the bouncing ball and after a few minutes a fresh installation.
After a quick run through the set-up I checked the version in Settings: pie test build, mission accomplished!
Notes
When wiping and formatting in twrp I noticed one red line of text at the head of output text, something like “E: unable to decrypt FBE device”. Not sure about that. If it was a valid error could it be that which made the factory reset necessary at the recovery stage?
Also in twrp, when selecting rebooting to recovery, there was the usual warning about “no OS present” to be ignored.
Just a thought, but I’m tempted to try a temporary Lineage recovery to install /e/ next time and see how that goes. But I have to say I’m pleased with the outcome today; it was quite painless. Apart from a few seconds of bootloop terror towards the end