Incomplete for loop in Try/Except in Python after adding additional operations

Suppose I have the following list of nested lists named val.

This is the original code:

val = [[63, 59, 47], 54, [59, 54, 47], [66, 59, 54], [65, 61]]
a = []
for i in range(len(val) - 1):
    #multiple notes at the same time
    try:
        if len(val[i]) > 1:
            for j in val[i]:
                if len(val[i+1]) > 1:
                    #multiple to multiple
                    print(val[i+1])
                    for k in val[i+1]:
                        print(k)

    except:
        print('not importent')

Result:

not importent
not importent
[66, 59, 54]
66
59
54
[66, 59, 54]
66
59
54
[66, 59, 54]
66
59
54
[65, 61]
65
61
[65, 61]
65
61
[65, 61]
65
61

What I found interesting is that if I add other operations like a[0] = 1 after print(k) in the try block, print(k) is only executed once, and not printing integers exhaustively

val = [[63, 59, 47], 54, [59, 54, 47], [66, 59, 54], [65, 61]]
a = []
for i in range(len(val) - 1):
    #multiple dots at the same time
    try:
        if len(val[i]) > 1:
            for j in val[i]:
                if isinstance(val[i+1],int):
                    #multiple to one
                    print('single value')
                elif len(val[i+1]) > 1:
                    #multiple to multiple
                    print(val[i+1])
                    for k in val[i+1]:
                        print(k)
                        a[0] = 1

    except:
        print('not importent')

Result

not importent
not importent
[66, 59, 54]
66
not importent
[65, 61]
65
not importent

Can anybody explain why this happens? and how can I make the for loop complete even if I add more operations after print(k)?