[Python] re.search() raises recursion depth error when in thread

In MicroPython, re.findall() does not exist. Therefore, I made one myself:

def findAll(pattern, s, flags = 0):
found = []
while True:
m = re.search(pattern, s, flags)
if m:
g = m.groups()
s = s[m.span()[1]:]
found.append(g[0] if len (g) == 1 else g)
else:
return found


This works well in all my tests, equally in cPython and uPython. However, in uPython, when called from a separate thread (Pico-W), I get an exception that I do not understand:

File "src/platforms/utils.py", line 16, in findAll
RuntimeError: maximum recursion depth exceeded


(line 16 is the first line in the loop, m = re.search(...))

The pattern is '\x01\x05\x02(.+)\x03\x04'; the searched string one or more repetitions of the pattern with a JSON-like string in the middle.

What might be causing this and how to solve it?

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