Chinese input very annoying on iOS 15.1

Just upgraded my ipad to 15.1 but found the Chinese input (pinyin) behavior to be extremely annoying from time to time. The symptom is that once I typed in some words, pressing space or clicking the words on the input bar does not make an effect (normally the words would be put in the input box). And I had to clear such words and type in one Chinese character and put the character in the input box.

the behavior happens from time to time and I have no idea why and when this happens. Never happened to me in past iOS versions.