5G Auto does not always switch to LTE when the 5G signal is weak. In 5G Auto mode, an iPhone will switch to LTE automatically when 5G speeds do not provide a noticeably better experience, which is intended to save battery life[4][6][8]. However, the threshold for switching from 5G to 4G can vary between different iPhone models, with some users reporting that their iPhone 14 models do not switch as readily as their iPhone 12 or 13 models[6]. In areas where the 5G signal is weak, the iPhone 14 might remain connected to 5G, even if the performance is poor, leading to a loss of data transmission[6].
Some users have also reported that their phones lose all network connectivity for a few seconds when automatically switching between 5G and LTE[7]. Others have found that forcing their phones to use only 4G or LTE provides a more stable connection[1]. Additionally, keeping the phone in "5G On" mode may result in dropped calls[4].
Citations:
[1] https://community.sony.co.uk/t5/xz-series/auto-switching-between-wifi-2-4ghz-and-5ghz/td-p/3587941
[2] https://www.reddit.com/r/iphone/comments/1bfe2in/iphone_constantly_switches_from_5g_to_lte_even/
[3] https://patents.google.com/patent/CN104168617A/en
[4] https://www.telecomhall.net/t/should-i-turn-5g-on-or-auto/22175
[5] https://xdaforums.com/t/what-makes-a-device-auto-switch-to-5g-or-lte.4374839/
[6] https://discussions.apple.com/thread/254828830
[7] https://www.reddit.com/r/Visible/comments/svwg5y/losing_all_network_connectivity_when_auto/
[8] https://support.apple.com/guide/iphone/view-or-change-cellular-data-settings-iph3dd5f213/ios