I just remembered that there is a には which can not be replaced by に or は. It's similar to にとっては, which might fit better here. e.g.
This kind of には is inherently contrastive so you always use は. (But にとって is still contrastive without は, it's a litter hard to explain.)
Whether this には in included in the scope of the subordinate clause is a little tricky. You can say something like:
But you can definitely use it in subordinate clauses without dropping the は.
I can't find much explanation in dictionaries. 大辞林 has only a single line for it:
But it's not clear if this には is に + は, e.g. people say
大辞泉 does not mention this usage.
The following is a part of the original answer.
I personally believe “topic は” cannot be solely semantically defined, because I can't find reasonable criteria and even Japanese linguists seem to disagree on the scope of “topic は”. e.g. some linguists consider “には” and “では” as “contrastive は”, while some think they are “topic は”.
If we talk about the “topic は”, I think we usually means:
It's often used in the main clause and can't be omitted
It's often not used in subordinate clauses.
For other kinds of は, they may freely appear in relative clauses.
The structure of your sentence can be understood as follows
In this sentence, the は appears in a subordinate clause, so it's not likely to be a topic は.
I also think “contrastive は” is the origin of all other はs. Different はs may functionally overlap so it's possible a single は has several functions or several different は appears in the same sentence.
Arguably “topic は” is always contrastive, because everything is different.