Playing blackjack 1 hand at a time v. 3-5 hands at a time same table?

I have been a blackjack player less than 10 days after playing poker for years.

My first three sites... Sites #1-3

I had the option of only playing one hand a time at the table.

Sites #4, 5

The last two sites I played three hands against the dealer at once and the second I played five hands a time against the dealer.

I have lost several more bets when I was playing Sites #4, 5 when playing multiple hands a time against the dealer.

I used the proper strategy charts on all 5 sites and I never increased my bets at any point on any site.

Thanks for reading this. I am not an expert on blackjack by any means but I noticed I have been doing much better 1 on 1 against the dealer as opposed to 3 on 1 or 5 on 1. I understand this could be a short term statistical anomoly.

I am curious if anyone else has experienced this. Thanks