jsonGet() expression function doesn't work with leading numbers in path segments.
In this demonstration expression below, neither "item.0" or "item.0L" work. "item.L0" does.
jsonGet("{'item':{'first':1, 'second':2, '0':3, '0L':4, 'L0':5}}", "item.L0")
Equivalent addressing via scripting works fine though:
test = {'item':{'first':1, 'second':2, '0':3, '0L':4, 'L0':5}}
print test['item'][str(0)]
print test['item']['0']
print test['item']['0L']
Each of those works as expected.
Tested in 8.3.2 (b2025120210) for reference.