When a stream is opened for both reading and writing, you are not allowed to directly switch between reading and writing. §7.21.5.3 ¶7 of the ISO C11 standard states the following:
When a file is opened with update mode (‘+’ as the second or third character in the above list of mode argument values), both input and output may be performed on the associated stream. However, output shall not be directly followed by input without an intervening call to the fflush function or to a file positioning function (fseek, fsetpos, or rewind), and input shall not be directly followed by output without an intervening call to a file positioning function, unless the input operation encounters end-of-file.
If you remove the line
fseek(file, 0, SEEK_CUR);
then your program violates this rule, which invokes undefined behavior. This means that anything can happen, which includes the possibility of your program getting stuck in an infinite loop.