I have a new never seen my me issue. I have a MRC DCC system I run mostly esu decoders I have a Digitrax dz126 decoder that when the engine is run alone it runs great but when in a consist it goes at half speed on all setting like it is in yard mode tho it is not. I have tried different consist numbers reset the decoder used a different numbers for the engine check cv 54 i think it is set to 0. nothing seems to work and it is only this decoder that has the issue. this is the only engine it has been in and the only setting that have been changed are cv256 for speed set up and cv3,4 for the acel and decel rates which all work great till is is set in a consist which is cv19.
I think you meant forget s setting lol but i did not do any setting in advanced exctept 21 and it is set to 134 for f8 and f2 (engine and horn) I set it up the same as all the others and it still is funny acting.
Try resetting your command station to clear the consist and try again. if that fails, reset the decoder (CV8=8), then turn off BEMF, then try again.
I would then contact Digitrax telling them you have reset both. Could be a bad decoder. Do you have another loco with a Digitrax decoder to try? Or, bring the loco to a friend or club with DCC and try to consist it to see if the issue follows the decoder.