When in doubt, consult the powder source's published data. In this case (W231) it can be found at the Hodgdon website.

Cartridge: 9mm Luger Load Type: Pistol Starting Loads, Maximum Loads
Bullet Weight (Gr.) Manufacturer Powder Bullet Diam. C.O.L. Grs. Vel. (ft/s) Pressure Grs. Vel. (ft/s) Pressure

115 GR. LRN Winchester 231 .356" 1.100" 4.3 1079 28,400 CUP 4.8 1135 32,000 CUP
115 GR. SPR GDHP Winchester 231 .355" 1.125" 4.7 1075 25,300 CUP 5.1 1167 28,100 CUP

Going by this data and your report, your 3.9 grain load is too light to produce sufficient recoil impulse for functioning your pistol.

You'll find little published data for plated bullets, so it's useful to treat them as somewhere between jacketed and cast. Accordingly, you might want to start between the two loads Hodgdon lists: 4.3 gr. (cast) and 4.7 gr. (jacketed). So, 4.5 grains should be reasonable starting for 115 grain plated bullets, with maximum of ~5.0.