During the production of the new ATLAS18 Inner-Tracker strip sensors for the forthcoming High-Luminosity Large Hadron Collider upgrade, the collaboration observed indications of low p-stop doping in a few sensor batches. Detailed studies of Quality Assurance test structures, such as MOS capacitors with p-stop or Punch-Through Protection structures, showed deviations of parameters dependent on the p-stop doping, observing also inhomogeneity within some of the wafers. Quality Control measurements of full-size sensors from these batches also showed indications of sensor areas with low inter-strip isolation. Although these sensor batches were identified and rejected, the performance of sensors with low p-stop doping after irradiation needs to be evaluated in detail to understand the possible consequences in working conditions. This work presents a complete characterization of the inter-strip characteristics of full-size and miniature ATLAS18 Inner-Tracker strip sensors irradiated with gammas and neutrons, covering a wide range of doses and fluences to study the influence of the ionization and displacement damages on the characteristics of the sensors with defective p-stop isolation. The radiation levels ranged from one equivalent to the first days of the ITk detector in working conditions to the end of the 10-year lifetime of the experiment. The sensors with low p-stop doping show a faster decrease in the inter-strip resistance than those with standard doping at all irradiation levels. Furthermore, results from miniature sensors irradiated only with gamma doses show that those with low p-stop doping fall below the ATLAS specifications much earlier than sensors with standard doping. In contrast, we observe that neutron irradiations increase the inter-strip resistance values for fluences above 4 × 1 0 14 n eq cm − 2 , suggesting that displacement damage dominates over ionization impact for fluences accumulated after only a few months in working conditions, improving the inter-strip isolation and compensating for the deficiencies of low p-stop doping.