The problem is that Ap's Export Masters command exports JPEGs with the metadata in XMP sidecars. Adobe apps have always assumed that JPEGs and other documented file types will have the metadata inside the image, not in a sidecar. So Ap is incorrectly creating sidecars, while LR is unhelpfully refusing to read them - I have asked for an option to make it do so, and exactly for this purpose.
OK, you do need to handle JPEGs separately from raw files. One option is to go via another program. iView/Expression Media can read the sidecar data, and can then write metadata directly into the JPEG, which LR can then read.
Another option for JPEGs is to use Export Versions instead of Export Masters. Assuming you want those JPEGs to look like the originals - ie not have Ap adjustments - you would need to remove all the adjustments before using this command.
If you really want the final result to be the original JPEGs with metadata in LR, you could do it in 2 steps. First an Export Versions to a single folder. Import it into LR, so LR now has the metadata, but the wrong JPEGs. Then - in Finder - delete those JPEGs. Go back to Ap, and do an Export Masters (without the sidecar) into the same folder. LR's records are now pointing to the original JPEGs. I'd tidy things up by doing a CmdS in LR, so the JPEGs now have the metadata. I'd add that I said one folder purely to keep things simple. I'd also do it in a test catalogue first. Once you understand the principles, you can then add complications.
John
