Same happened to me repeatedly at QR counter in BKK. Once I was carrying really special Virtual Reality headset and I have had troubles repacking everything. No way I could but this utterly expensive device on hold. Then you see the empty bins on the plane. Ridiculous. Never happened to me in EU travelling the reverse way to BKK. Actually I wonder what would happen if I check in w/o small bag and later on take my stuff onboard, because I did not see anybody checking the weight at the gate.

And really nice cultural experience is trying to argue with Thai checkin staff. They keep smiling, understand your emotions, agree with whatever you say and at the end when they agree with you .... there is just a result NO.