Last night one of my Roamio boxes ...

4-tuner or 6-tuner? And ideally what model TCDxxx?

... woke up from standby...

Don't use standby.

...Could this be a drive issue ? A power supply issue ? ...

It could be either, but if it's a 4-tuner Roamio ("Roamio OTA" or just plain "Roamio") I would first check the output voltage of the external Power Adapter under load using a "Y-cable" or "splitter cable" and a DC voltmeter. Or just replace it with a good-quality external Power Adapter, and not just the cheapest you can find.

Or if you have multiple 4-tuner Roamios, you could swap Power Adapters and see if the problem behavior stays with the Roamio currently having a problem, or moves with the Power Adapter originally in question.

It is not rare for 4-tuner Roamios to eventually have problems with the original TiVo-supplied Power Adapter, and I would suggest replacing each such original Power Adapter with a good-quality aftermarket Power Adapter before waiting for it to degrade enough to cause operational failures.

For a 4-tuner Roamio you need 12VDC, 5.5x2.1mm barrel connector compatible, center positive polarity, at least an honest 2 Amp rating, and reviews with few or no reports of early failures, and no reported instances of safety problems like falling apart, melting, catching on fire, or wires breaking. Many cheap external Power Adapters on Amazon (or elsewhere for consumer-grade products) do not have honest amperage ratings, since it is cheaper to print a high rating than to actually provide it. On Amazon, I like the Chanzon 5A or 3A models, and don't like the Facmogu. The start of a relevant discussion string: Replace Roamio Hard Drive - or use search.

 

A restarting Tivo almost always mean a bad hard drive when it cannot get past the "almost There" screen.

If a Roamio has the All Blinking lights, it usually mean the external power supply is failing (usually its a 4 tuner model)

 

I tried trouble shooting my Roamio with this same issue and gave up. The original drive works fine, but the original expanded drive I created causes an endless cycle of reboots, as does a drive I created from that image (hoping to save the recordings). I tried using an external power supply connected to the drive, but that didn't resolve the issue. I really think that something just got corrupted on the expanded drive that TiVo cannot work past, and whatever that corruption is got copied over to the new drive. Because I didn't want to risk expanding the original drive again to a larger drive and then have the same reboot loop, I just put my Romaio out of service and started using my Premiere again with an expanded drive.

 

Your problem is using 2 drives which is a bad thing. If anything fails, either drive or the connection, then you have these problems.
Its best to use a single and larger drive and stop using the external drive with the internal one. Using an external drive, the shows get stored on both drives and you lose them when either fails.

Roamio can self-format a new drive, up to almost 3 TB on TE3 (Blue background menu color), or all of the space in TE4 (Black menu background), but TE4 loses some features and introduces others. This method makes the Tivo as a new unit.

To keep the settings and recordings, you need to use MFSTools to copy the drive and expand it to full capacity. You can download unprotected shows to a PC, and later re-upload back (TE3 only).

 

my Roamio is 13 years old & eventually something unrepairable will happen or get fried by some electrical goblin … very few devices last this long and are still usable… when it goes it will be a sad day