This may be caused by a conflict between the ntheorem package and the amsthm package.

Solution: don’t use both, just delete the reference of one package.

Note that some template class files (.cls) may introduce one of the packages in advance. For example, the template file (ccjnl.cls) of China communication introduces the amsthm package in advance

At this time, you can only use the amsthm package instead of the ntheorem package.