Yes, that's what I'm doing. It's a simple interface.
The iPad error doesn't given an error code, just the message in the topic line. I only mentioned the iPhone problem as evidence that Catalina causes the problem. Apple's list of error codes doesn't include 50 (-50), the iPhone error. So no help there.
When I plug in the iPad (Et tribus, Rob?), then hit sync, the system log shows these messages that are apparently all related to the iPad:
default 15:47:22.103683-0800 rapportd BLE device changed: SFDevice ID 8d75fc9b-7d7e-481b-a86c-f7f2657371b2, IDS 455AB9F5, RSSI -33 (-28)*I, Nm 'Et tribus, Rob?', Md 'iPad11,3', AID 'rob.mathews@stanfordalumni.org', DuetSync, rapportID 455AB9F5-4C7E-4B49-830F-037BE4459AFD, WiFiP2P, DF 0x82 < Family AirDrop >
default 15:47:22.103761-0800 rapportd BLE device changed: SFDevice ID 8d75fc9b-7d7e-481b-a86c-f7f2657371b2, IDS 455AB9F5, RSSI -33 (0)~U, Nm 'Et tribus, Rob?', Md 'iPad11,3', DuetSync, PairedSys Conjectured, rapportID 455AB9F5-4C7E-4B49-830F-037BE4459AFD, WiFiP2P, DF 0x80 < AirDrop >
default 15:47:22.103827-0800 sharingd CompanionLink changed: IDS 455AB9F5, Nm 'Et tribus, Rob?', Md 'iPad11,3'
default 15:47:52.823626-0800 rapportd BLE device lost: IDS 455AB9F5-4C7E-4B49-830F-037BE4459AFD, Nm 'Et tribus, Rob?', Md 'iPad11,3'
default 15:47:52.823658-0800 rapportd BLE device lost: IDS 455AB9F5-4C7E-4B49-830F-037BE4459AFD, Nm 'Et tribus, Rob?', Md 'iPad11,3'
default 15:47:52.823780-0800 sharingd CompanionLink lost: IDS 455AB9F5, Nm 'Et tribus, Rob?', Md 'iPad11,3'
default 15:47:52.823813-0800 sharingd Device lost never had hotspot info: IDS 455AB9F5, Nm 'Et tribus, Rob?', Md 'iPad11,3'
Any insight from that? What does "hotspot info" refer to? The hotspot on my iPhone that I sometimes connect the iPad to? Just for fun, I turned on the hotspot on the phone. Unsurprisingly, that didn't fix the problem. The log is a little different, though:
default 15:52:50.839709-0800 rapportd BLE device lost: IDS 455AB9F5-4C7E-4B49-830F-037BE4459AFD, Nm 'Et tribus, Rob?', Md 'iPad11,3'
default 15:52:50.839812-0800 rapportd BLE device lost: IDS 455AB9F5-4C7E-4B49-830F-037BE4459AFD, Nm 'Et tribus, Rob?', Md 'iPad11,3'
default 15:52:50.839932-0800 sharingd CompanionLink lost: IDS 455AB9F5, Nm 'Et tribus, Rob?', Md 'iPad11,3'
default 15:52:50.839961-0800 sharingd Device lost never had hotspot info: IDS 455AB9F5, Nm 'Et tribus, Rob?', Md 'iPad11,3'
default 15:52:53.648531-0800 rapportd BLE device found: SFDevice ID 3cd4fcd5-569f-4628-a4bc-118b6cbf7763, IDS 455AB9F5, RSSI -37 (0)~U, Nm 'Et tribus, Rob?', Md 'iPad11,3', DuetSync, PairedSys Conjectured, rapportID 455AB9F5-4C7E-4B49-830F-037BE4459AFD, WiFiP2P, DF 0x80 < AirDrop >
default 15:52:53.648529-0800 rapportd BLE device found: SFDevice ID 3cd4fcd5-569f-4628-a4bc-118b6cbf7763, IDS 455AB9F5, RSSI -37 (0)~U, Nm 'Et tribus, Rob?', Md 'iPad11,3', AID 'rob.mathews@stanfordalumni.org', DuetSync, rapportID 455AB9F5-4C7E-4B49-830F-037BE4459AFD, WiFiP2P, DF 0x82 < Family AirDrop >
default 15:52:53.648648-0800 sharingd CompanionLink found: IDS 455AB9F5, Nm 'Et tribus, Rob?', Md 'iPad11,3'
default 15:52:53.648674-0800 sharingd Found device without hotspot info: IDS 455AB9F5, Nm 'Et tribus, Rob?', Md 'iPad11,3'
The iPad itself is Wi-fi only, so of course it has no hotspot of its own.
Rob