Still dealing with German roaches — need advice on spray cadence

Single-family home. Sister moved out of an infested apartment and unfortunately brought a heavy German roach infestation with her. Her belongings were now removed and in storage about 2 weeks after discovering the infestation.

Treatment so far:

• Alpine WSG (30 g per gallon), sprayed every 7–10 days
• Gentrol point source pucks deployed
• Strategic use of baits (Advion, Raid dry bait)
• Glue traps used only for monitoring
• I've temporarily vacated the house to reduce food/moisture during treatment (also have toddler who was very interested in sticky traps, bait pucks, etc)

After ~3 weeks of seeing no activity on glue traps, our exterminator advised stopping sprays and transitioning to bait + monitoring only.

About one week after stopping sprays, roaches reappeared.

Current observations:

• Activity seems centered in the kitchen island
  • No food stored there
  • Includes sink, dishwasher, plumbing, drywall voids
• Previously mostly nymphs; now seeing some adults + instars again

Questions:

1. How long should Alpine WSG realistically be applied in a situation like this? Is every 14 days for multiple months the right approach, even if activity appears to stop?
2. Is it normal to see a rebound like this after pausing sprays?
3. Any specific advice for treating an island/plumbing void harborage?

I’m trying to balance avoid over- or under-treating because I need to pay an exterminator to do this for various reasons. Appreciate any professional insight.