Update: In that test I had an uptime of 30 hours, using the phone well on wifi, calls and SMS. I lost the uptime due to coming indoors without switching wifi off, so I failed to do my “soft wifi connect”.
I did just note this post where an A310F… is reported running
I add this comment as I wonder if something in the Stock ROM still lingers from the phone previously locked to carrier O2?
#263.
I have searched for stock ROMs for this device, the carrier is still mentioned. I wonder if the same apples to SM-J700F j7eltexx which shares this issue #263.
(Meanwhile e-0.10-p-2020081067156-test-a3xelte updated with an update containing date 20200813 has run nicely for over a month and 24 hour test of lineage-17.1-20210103-recovery-a3xelte.img - no issues found.)