OK, let's unravel this dump. First off, "000003C4 : B6FC0B52" makes little sense because it would indicate an exception 0xB6, which does not even exist. But let's not get distracted by this and assume this is a line F exception (0x0B) like you saw before. Decoding the exception frame on the stack...
000003CC : 2304
000003CE : 7020
000003D0 : 0000
... shows that this exception occurred at PC=0x70200000, in line with what you saw before. (On the address bus you only see 24 bits of the PC.) Notice the most significant byte of the PC (0x70), this will get important in a moment.
So, how did you end up there? Let's follow the stack further:
000003D2 : 00FC
000003D4 : 9C28
This looks like a return address, and indeed it is:
00fc9c20 20 6e ff ce movea.l (local_36 ,A6),A0
00fc9c24 20 50 movea.l (A0),A0
00fc9c26 4e 90 jsr (A0)
00fc9c28 58 8f addq.l #0x4 ,SP
This is in the GEMDOS function dispatcher, where GEMDOS jumps to the requested function, depending on its number. Of course, it should never end up at PC=0x70200000, though. Let's look where it presumably jumped to:
000003A4 : 700113C0
This is A0, the jump address -- assuming that this register was not modified since. Notice again the 0x70, so we seem to be on the right track.
But how can the GEMDOS function dispatcher jump to 0x700113C0 in the first place? The dispatches uses a table of function pointers from ROM but none of these of course points to 0x700113C0. But notice how 0x7001 0x13C0 looks like valid opcodes: MOVEQ #1,D0; MOVE.B D0,something.
In TOS 1.02 (German) the function pointer table goes from 0xFD30D4 to ca. 0xFD32DE. And at 0xFC3296 we have: 0x700113C0!
While I made some assumptions along the way, this deduction still seems to indicate to me that your MegaST is somehow reading from the wrong address in ROM sometimes.
EDIT: I only see it now. You even have 0xFD3296 on the stack, further corroborating my deduction. So, the GEMDOS dispatcher meant to read from 0xFD3296 (which is a pointer to Pexec(), BTW) but it read from 0xFC3296, which is a pointer to essentially nowhere.
EDIT2: Tracing with Hatari shows that in TOS 1.02 Pexec() is indeed the first GEMDOS function being called in this way. So this makes sense.