there's currenlty a size-limit of 0,5 MB for the resultng GPX in a service call to BRouter
To workaround that limit, I added a compression option to BRouter 1.5.x, where the GPX is gzip/base64 encoded internally.
For the client-side patch see this OsmAnd-PR:
Could you implement this for Locus as well?
thanks for pointing on this nice improvement. Implemented. Will be right in next version next week.