My findings are similar to what some others have reported.

I tested TUBE on the latest version 0.33b5 on two different identical rigs, each with 6 x  8GB RX 580, with the only difference being one is on Adrenalin 18.6.1 drivers and the other is 18.5.1.

With each rig, only one GPU out of 6 reaches maximum hashrate (approx 1220 h/s), and the other 5 GPUs level out around 990 - 995 h/s. I have tried various multihash settings as well as other greeks but this issue remains regardless.

If I use the --no-warmup switch, 3 (sometimes 4) of 6 GPUs (for both rigs) will reach maximum hashrate (up to 1180 h/s) and the others will remain in the upper 900s h/s.