Hello everyone!
So I assume the problem arises when using the bot for several games, because the win rate is lower than playing yourself (no offense, its a very good bot, but normal human opponents are normally better under same circumstances in comparison)
When your win/loss ratio now drops compared to normal human players, you are most likely matched other bots as well.
And this is the point, These other bots as you already mentioned are not as good at yours, which means their play pattern is easily detected and leads to the annulation of the win and the aforesaid meassage.
I make this assumption based on the following observations;
1.) I get credit and gold with the bot for wins when having a higher win/loss ratio (e.g. after playing myself several games or the bot being lucky and winning more games than usual)
2.) I don't get credit or gold for wins even if I play myself without the bot after loosing several games in a row, so when my win/loss ratio is low.
3.) When having lost several games it seems I am facing mostly bots I can easily detect (no emotions, no arrows, obvious unlogical mistakes and so on)
For me this is the best explanation I could figure out at the moment, since we do not know how your matchmaking rating is calculated exactly (as far as I know). If you have any other observations, explanations, theories or corrections etc. please let me know ;)
... and sorry for the lenghty speech, I should really learn to cut it short, but otherwise I feel I could be misunderstood :P