I have found this in ublox manual. I think some Problems would be solved with a cold restart.
4.2.1 Switching between GNSS
Users should be aware that switching between GNSS (and especially away from GPS) may affect the long term accuracy of the receiver until the next cold start. In normal operation the receiver selects the best models and corrections from the transmitted auxiliary data (e.g. UTC and Ionospheric parameters), basing this selection on the configured GNSS. Disabling a major GNSS prevents auxiliary data from that GNSS being refreshed and so it will become stale, resulting in progressively degraded performance. This can occur even if the main power supply is removed, as most receivers retain auxiliary data in non-volatile storage, e.g. Battery Backed RAM (BBR). For this reason, u-blox recommends that receivers are cold started after any change that disables an active GNSS, within a few weeks, but preferably immediately. This will ensure that the receiver then uses only regularly refreshed information from the newly configured constellations.