This means that not the number of columns and rows respectively the size of the data-set and/or the complexity of the content is causing the issue else it looked that there is any incompatibility between the object and the Excel export-libraries. I'm not absolutely sure but nearly no tool will use for it own libraries else MS standard libraries. So it's rather unlikely that Qlik could fix anything or providing a special support.
IMO most likely for such behaviour is any invalid evaluation within the object - especially within the meta-data. Means extra calculations for conditions, labels, title, colors but also dimension/expression-groups and so on which may return NULL and/or any error and/or are empty and the library couldn't handle it and the export-routine crashed. Even it's seldom there is also a probability that the object is corrupt in some way (created within other major-releases, copy & paste from different applications, multiple type-changes of the object, ...).
To find such issues could be quite hard. Therefore I suggest to re-create the object from the scratch. Copy and paste from the expressions - maybe with an intermediate editor - is ok. but no copy & paste of any properties. Even by 20 columns it's take not long and after each 3 columns you tries to export. Now you will see fast where it breaks or not and if you could look if the cause could be fixed ... and step by step you extend your object again ... or when you found the cause you may fix it within the origin object.
