Right, thanks for surveying. The fact that the church access road was previously 5mph would surely mean that
 (a) it’s a private road (I don’t believe 5mph speed limits exist or are valid on any public road) and
 (b) if the 5mph sign is still there then the speed limit on that road is 5mph, even if it’s within a 20mph zone?

In https://www.openstreetmap.org/changeset/171457594 you added maxspeed:advisory=5mph, but I think maxspeed=5mph would be better for it. aiui, maxspeed:advisory is meant for advisory speed limits on bends (sign: https://www.drivingtesttips.biz/images/recommended-speed-limit.jpg). See https://wiki.openstreetmap.org/wiki/Key:maxspeed:advisory