Detecting runtime random errors in a C program that don’t reproduce in a slow debug build can be challenging. Here are a few techniques that can help you diagnose such issues:

1. Enable debugging symbols: Make sure that you compile your program with debugging symbols enabled (-g flag in most compilers). This allows you to get more detailed information when an error occurs, such as line numbers and variable values.
2. Use runtime analysis tools: Utilize tools like AddressSanitizer (ASan) or Valgrind to detect memory errors, such as buffer overflows, use-after-free, or uninitialized memory access. These tools can help identify memory-related issues that may lead to random errors.
3. Log relevant information: Insert print statements or logging code at critical points in your program to output relevant information. This can include variable values, function calls, and any other relevant details that might help you understand the state of your program when the error occurs.
4. Reproduce the issue with test cases: Even if the error seems random, try to isolate the conditions that trigger it. Create test cases that exercise different parts of your code and try to narrow down the circumstances under which the error occurs.
5. Use defensive programming techniques: Review your code for potential issues, such as uninitialized variables, incorrect memory allocations, or incorrect usage of pointers. Apply defensive programming techniques like input validation, error checking, and boundary checks to catch and handle potential errors.
6. Divide and conquer: If your program is large and complex, try to isolate the problematic code or module. By systematically disabling or isolating parts of the program, you can identify the specific code section responsible for the error.
7. Time-based debugging: If the error occurs randomly but can be triggered within a specific time frame, you can insert time-based checks or delays in your code to allow you to observe the program’s state when the error occurs.
8. Seek help from others: If you are unable to identify the root cause of the random error, consider reaching out to forums, communities, or colleagues who may have experience with similar issues. Sometimes fresh eyes or different perspectives can help in diagnosing the problem.

Remember, debugging random errors can be time-consuming, and it often requires patience and perseverance. It may involve a combination of techniques and multiple iterations to identify and resolve the issue.