I got an answer from Elektron for a ticket I sent regarding this issue… and behold option 3:
If you set RLEN in rec setup 1 to a number value (for example 64), and PLEN on rec setup 2 to the same value… it works!!! you can record your first (master) pickup machine at 70 BM, and it won’t change the tempo after looping 
overdub works too
so drawback is you have to pre-set your loop length, and maximum is 64 unfortunatly. but it works.
Cool will try t out.
Good to know. Could you also try to disable timestretch in Attributes (after recording maybe) to make it work?
Maybe a tempo change needed after recording…?
I don’t understand… are you talking about pickup machines?
Yes, Pickups. Apparently, if you set Playback Setup > Timestretch Auto and set Attributes > Timestretch OFF, after recording, you can theorically get original tempo.
@polite_society pointed that, I think it’s an interesting possible workaround. I can’t test unfortunately, if nobody do it I’ll do it, but I work too much to find the energy for that.
yes, but you can do this only after recording and after bringing the tempo back down.
it will still double the tempo initially after recording the loop… so for playing live this is not an option.
Yes of course not satisfying, but I was thinking about your project with DT.
So I am still fighting this issue. I have replaced 2 guitar loopers and a boss rc-505 for looping mics and percussion with the octatrack. and all fx slots, master track fx and scenes makes me want to stay looping in the octatrack!! those 3 loopers only cost almost as much as 1 octatrack, so I can justify making 1 big looper out of it.
so… I ended up buying the audio werkstatt midi clock divider (https://www.audiowerkstatt.de/en/midi-clock-divider-v2). works like a charm to let the OT operate as a double tempo master and send ‘normal’ bpm to the other devices. BUT… because the OT tempo comfortable zone is in between 85 and 170 bpm, when I want to play faster songs, it halves the tempo again! so when I put the OT at 170 (so it sends 85 to the rest), after looping it will jump back to 85 (and send 42,5 to the rest!)
so now when I want to play 85 bpm and higher, I have to put the tempo divider on 1/1 so it sends the same clock. 1 more implication is that I set the metronome to 2/4 when I play at double speed, and now I should have to change that back to 4/4 as well if I want a normal metronome…
this is getting pretty complicated 
but hey, it works…
so now I was thinking. what if I set track 7 as dummy master pickup. use the above trick to set RLEN and QPL to 16, record one bar of silence and have a master pickup running at 75 BPM. so far so good, this works. now I understand that in theory if I record a second pickup machine, this would be a slave, and follow the tempo of the paster pickup machine right? it does not… jumps to 140 BPM is there anything I am missing???
Is the master pickup loop still running when you start recording with the slave pickup machine?
Is the master / slave relationship as you think it should be (first master, second slave)? The track icons indicates which one is the master and which one is the slave.
Difference between Master and Slave Track Icons:
Two pixels located at the top left side of the “P” indicate a master Pickup machine. Two pixels to the bottom left indicate a slave Pickup machine.
Yes, I record the master and it has the master pixels. Immediately after, when the master is playing back, I record a second one. I did notice that the second pickup machine isn’t always showing the lower ‘slave pixels’… I’ll play around with this a bit and report pixel behaviour
ok, so when I have a masterpickup machine running, and I run another pickup machine with LEN in theSRC page set to “OFF”, the tempo doubles and there is no pixel in front of the P… if I set the LEN to anything else then OFF, it becomes a slave pickup as expected and shows the lower pixel in front of the P. and the tempo does not change…
so there are ways to make it work, but as I rely a lot on improvisation, I don’t know how long my loop will be… and there is no way to make it work in a setting where I can choose my loop length… with RLEN to max and LEN to off…
I think I will give up
I decided to go for the complicated tempo divider route and jam a little bit. I was jamming at 90 BPM so there wasn’t even a problem with the tempo range… everything went well for the first 5 loops, and then recording the 6th loop, the tempo jumped from 90 to 120… with no reason at all. rec quantize and play quantize are both set to a bar. All tracks except 8 (master) are identical pickup tracks…
I guess I’ll try the route of an empty dummy track and then set a fixed length on the pickup machines. but if I can’t deal with fixed loop lengths or another solution pops up I will have to bring back the guitar loopers and rc-505, which would be a real bummer
Flex route? That the one I took quickly, coming from RC505 (also Rc202, RC300, RC50), KP3…
I tried that, and at least it works but the way I did it I was bound to a pre set length as well, and that is what I am trying to avoid.
Now I installed my infinity looper for guitar and rc-505 for instruments again, and route them to the inputs of the OT. With thru tracks I can still do quite fun things with the loops, and I also can still use flex or pickups to capture those looper’s. I want to be able to loop quickly on the fly, without knowing before what I will do, so setting up very complex systems in the OT won’t work for this… I think I can manage with this setup now at least I am looping again and having fun!!!
Quantized recordings let you record with undefined length. Recordings can be played looped with a plays free track, or 1ST TRC…
I’m trying 1ST now…
Edit : not satisfying. Arm one shot trig can be interesting too.
I had fun looping and overdub with Flex! 
Of course RC505 is much more direct / simple / intuitive…
Interesting, I haven’t thought of looping with flax and plays free tracks. Have to try that
Yeah it’s interesting to experiment more Flex anyway. One recorded, maybe it’s easier to trigger the recording with QPLAY, rather than play free tracks.
I’m still waiting for a looper between OT and RC505…
yes!!! which would be an OT with functional pickup machines, but since they’re not, such a device would be awesome
And I will see how I can play with flex now. I have the loopers setup, so I can do whatever I want and play, and if I feel like I can skip them and try looping with flex machines (since they’re routed into the OT anyway)