Present and past participle in same sentence

Is anything wrong about this phrase "We build software solutions designed for scalability"? I think there is, because the tenses are not consistent.

There is absolutely nothing whatsoever wrong with that sentence. A participle that introduces a verbal phrase is under no obligation to agree with the tense of the main verb. That just would not be sensible.

Examples of the past participle used with non-past verbs:

• We’re looking for people interested in birding.
• English is the world language spoken by the most number of individuals as a second language.
• I won’t fix a roof damaged by hail.
• You should drink only water boiled for at least one minute.
• Broken windows must be repaired immediately.

Examples of the present participle used with non-present verbs:

• I saw you sleeping in the park.
• I always ate my ice cream with it dripping down my chin.
• I didn’t want him contemplating any other possibility.
• Running in the morning was never my passion.

Designed for scalability is a participle clause, postmodifying solutions. Designed is a non-finite verb, which means it shows no tense or person. The clause can be replaced with a finite relative clause with a passive verb: We build software solutions that are designed for scalability. That may help you understand why there is no inconsistency in the verbs.