Saw this recently in the Adobe forum:
NB:
The built-in proxies don’t work properly with time-remapped clips. There’s a way to do it though …
* In the Project panel, select the original clip/s that have been interpreted (time change) and need proxies
* Right-click, Proxies/create proxies; AME will launch, switch to that app immediately and …
* Stop the encoding process in AME before it finishes, and select that clip then right-click “Reset Status”
* Select (all clips, if working a number of them), right-click and select “Interpret footage” setting the timebase to that of the modified originals;
* click the go-ahead arrow to process the proxies; when complete, all but the stopped/reset clip will show in PrPro as “attached” in the PrPro Project panel.
* For the clip that was stopped/reset, right-click on the original media clip/s in PrPro, right-click, “Proxies/Attach Proxies”
* Select the clip, then navigate to where the proxies are stored on disc, select, “attach” and voila.