A downgrade to the correct Android version via Lineage has been reported successful in some Samsungs recently.
If you can find the manufactures ROM this should work, if the device is down-gradeable like that.
In this case we can look at and compare the device trees at 18.1 and 19.1
18.1 https://github.com/LineageOS/android_device_motorola_ocean/tree/lineage-18.1
19.1 https://github.com/LineageOS/android_device_motorola_ocean/commits/lineage-19.1
We see 19.1 is 9 commits ahead.
In a quick search these commits are for the build, so do not lend themselves to patching direct to the device with your existing e-1.3-r-xxx-ocean
Depending how much sense this actually makes to you 
you might make a list of the ahead commits (might not accurately be the newest commits) that are actually in 19.1.
This might help inform a better clue as to whether the downgrade is the only route or if some sort of non-trivial patch might be applied as you reinstall e-1.3-r-xxx-ocean` over the 19.1 “foundation” which I guess you have existing.
ocean does appear on this list [LIST] Devices we plan to upgrade to /e/OS S
Perhaps also watch development-updates for news.