解決済! 解決策の投稿を見る。
About the instruction trace not showing anything else, you may have a point.
But, it's also possible that the stack is already full right before the CALL (sometimes), and that the return address is pushed into non-RAM, so that when it is retrieved by the RTC, it's "garbage".
Can you check where the SP is pointing right before the CALL and right before the RTC (and the corresponding memory contents)?
The word "sometimes" in your problem description almost certainly indicates stack corruption, which can occur not only by overwritten stack memory but also by an SP register pointing outside the stack, or outside all RAM.