import re
p = re.compile(r'Sample comments:\s*\[(.*?)\s*]')
s = " Sample comments:\n\n [98 g/m2 Ctrl (No IP) 95 min 340oC ]\n\n [ ]"
print(p.findall(s))
aW1wb3J0IHJlCnAgPSByZS5jb21waWxlKHInU2FtcGxlIGNvbW1lbnRzOlxzKlxbKC4qPylccypdJykKcyA9ICIgIFNhbXBsZSBjb21tZW50czpcblxuICAgIFs5OCBnL20yIEN0cmwgKE5vIElQKSA5NSBtaW4gMzQwb0MgICAgICAgICBdXG5cbiAgICBbICAgIF0iCnByaW50KHAuZmluZGFsbChzKSk=