Can accessing mutex over a loop result in __pthread_mutex_lock: Assertion `mutex->__data-__owner == 0' failed

Question

I have a function which is intermittently throwing the error

__pthread_mutex_lock: Assertion `mutex->__data-__owner == 0' failed.

From my research till now I came to know the following cases in which this deadlock happens (please correct me if I am wrong):

1. If a thread has locked a mutex and again trying to lock the same mutex.
2. If the mutex the thread is trying to lock is either not initialized or destroyed/corrupted.
3. Corruption of memory stack.

The function has several sections using mutexes but a senior of mine pointed out a particular section and asked me to look into it, though even he couldn't pinpoint the problem but I am trusting his intuition. This part is a for loop which is repeatedly calling a send() function which is writing data to a message queue. Though from my review of the code till now I couldn't find any way in which the code might hit case 1 or 2 all mutexes are properly locked and released. Which leads me to suspect case 3, but the problem is that case 3 is very rare, but the occurrence of the issue is not that rare. Hence I am requesting anyone with a better understanding to take look into the code and confirm whether it is safe to call the send() function over in a loop, if yes than what might be causing mutex lock error. Here is the pseudo code:

class SafeMutex{
pthread_mutex_t s_mutex;
public:
void lock(){
pthread_mutex_lock(&s_mutex);
}
void unlock(){
pthread_mutex_unlock(&s_mutex);
}};

SafeMutex mymutex;

int send(){

mymutex.lock();

if(Condition A){
    }
else{
    if(Condition B){
                mymutex.unlock();
                return 1;
        }
    }
          mymutex.unlock();
if(Condition C){
          mymutex.lock();
          
          if(Condition B)
          { mymutex.unlock();
            return 1;
          }
          mymutex.unlock();
          if(Condition C)
          { return 1; 
          }
     }
return 0;
}

void SendMessages() {
    for (i = 0; i < 30; i++) {  //this loop is calling send() with proper argument
        send();  
    }
}

PS: I am a noob still learning, please be easy on me :).

There is this question where the author has talked about lower level race condition in pthread_mutex_lock file, If anyone can tell further about this then it will be great: Pthread mutex lock assertion fails